diff --git a/cartographer/cloud/client/map_builder_stub.cc b/cartographer/cloud/client/map_builder_stub.cc
index 0690cc1..c326223 100644
--- a/cartographer/cloud/client/map_builder_stub.cc
+++ b/cartographer/cloud/client/map_builder_stub.cc
@@ -124,8 +124,8 @@ void MapBuilderStub::SerializeState(io::ProtoStreamWriterInterface* writer) {
   }
 }
 
-void MapBuilderStub::LoadState(io::ProtoStreamReaderInterface* reader,
-                               const bool load_frozen_state) {
+std::map<int, int> MapBuilderStub::LoadState(
+    io::ProtoStreamReaderInterface* reader, const bool load_frozen_state) {
   if (!load_frozen_state) {
     LOG(FATAL) << "Not implemented";
   }
@@ -163,6 +163,13 @@ void MapBuilderStub::LoadState(io::ProtoStreamReaderInterface* reader,
   CHECK(reader->eof());
   CHECK(client.StreamWritesDone());
   CHECK(client.StreamFinish().ok());
+  // TODO(gaschler): Return trajectory remapping.
+  return {};
+}
+
+std::map<int, int> MapBuilderStub::LoadStateFromFile(
+    const std::string& filename) {
+  LOG(FATAL) << "not implemented";
 }
 
 int MapBuilderStub::num_trajectory_builders() const {
diff --git a/cartographer/cloud/client/map_builder_stub.h b/cartographer/cloud/client/map_builder_stub.h
index d102cef..c60a4a8 100644
--- a/cartographer/cloud/client/map_builder_stub.h
+++ b/cartographer/cloud/client/map_builder_stub.h
@@ -48,8 +48,9 @@ class MapBuilderStub : public mapping::MapBuilderInterface {
       const mapping::SubmapId& submap_id,
       mapping::proto::SubmapQuery::Response* response) override;
   void SerializeState(io::ProtoStreamWriterInterface* writer) override;
-  void LoadState(io::ProtoStreamReaderInterface* reader,
-                 bool load_frozen_state) override;
+  std::map<int, int> LoadState(io::ProtoStreamReaderInterface* reader,
+                               bool load_frozen_state) override;
+  std::map<int, int> LoadStateFromFile(const std::string& filename) override;
   int num_trajectory_builders() const override;
   mapping::PoseGraphInterface* pose_graph() override;
   const std::vector<mapping::proto::TrajectoryBuilderOptionsWithSensorIds>&
diff --git a/cartographer/cloud/internal/client_server_test.cc b/cartographer/cloud/internal/client_server_test.cc
index 0fcf188..bf7e572 100644
--- a/cartographer/cloud/internal/client_server_test.cc
+++ b/cartographer/cloud/internal/client_server_test.cc
@@ -448,6 +448,8 @@ TEST_F(ClientServerTest, LoadState) {
   server_->Shutdown();
 }
 
+// TODO(gaschler): Test-cover LoadStateFromFile.
+
 }  // namespace
 }  // namespace cloud
 }  // namespace cartographer
diff --git a/cartographer/mapping/internal/testing/mock_map_builder.h b/cartographer/mapping/internal/testing/mock_map_builder.h
index 78e8af9..23b1fb4 100644
--- a/cartographer/mapping/internal/testing/mock_map_builder.h
+++ b/cartographer/mapping/internal/testing/mock_map_builder.h
@@ -48,7 +48,9 @@ class MockMapBuilder : public mapping::MapBuilderInterface {
                std::string(const mapping::SubmapId &,
                            mapping::proto::SubmapQuery::Response *));
   MOCK_METHOD1(SerializeState, void(io::ProtoStreamWriterInterface *));
-  MOCK_METHOD2(LoadState, void(io::ProtoStreamReaderInterface *, bool));
+  MOCK_METHOD2(LoadState,
+               std::map<int, int>(io::ProtoStreamReaderInterface *, bool));
+  MOCK_METHOD1(LoadStateFromFile, std::map<int, int>(const std::string &));
   MOCK_CONST_METHOD0(num_trajectory_builders, int());
   MOCK_METHOD0(pose_graph, mapping::PoseGraphInterface *());
   MOCK_CONST_METHOD0(
diff --git a/cartographer/mapping/map_builder.cc b/cartographer/mapping/map_builder.cc
index 3ad6de5..d0ba2df 100644
--- a/cartographer/mapping/map_builder.cc
+++ b/cartographer/mapping/map_builder.cc
@@ -19,6 +19,7 @@
 #include "cartographer/common/make_unique.h"
 #include "cartographer/common/time.h"
 #include "cartographer/io/internal/mapping_state_serialization.h"
+#include "cartographer/io/proto_stream.h"
 #include "cartographer/io/proto_stream_deserializer.h"
 #include "cartographer/mapping/internal/2d/local_trajectory_builder_2d.h"
 #include "cartographer/mapping/internal/2d/overlapping_submaps_trimmer_2d.h"
@@ -206,8 +207,8 @@ void MapBuilder::SerializeState(io::ProtoStreamWriterInterface* const writer) {
   io::WritePbStream(*pose_graph_, all_trajectory_builder_options_, writer);
 }
 
-void MapBuilder::LoadState(io::ProtoStreamReaderInterface* const reader,
-                           bool load_frozen_state) {
+std::map<int, int> MapBuilder::LoadState(
+    io::ProtoStreamReaderInterface* const reader, bool load_frozen_state) {
   io::ProtoStreamDeserializer deserializer(reader);
 
   // Create a copy of the pose_graph_proto, such that we can re-write the
@@ -364,6 +365,20 @@ void MapBuilder::LoadState(io::ProtoStreamReaderInterface* const reader,
         FromProto(pose_graph_proto.constraint()));
   }
   CHECK(reader->eof());
+  return trajectory_remapping;
+}
+
+std::map<int, int> MapBuilder::LoadStateFromFile(
+    const std::string& state_filename) {
+  const std::string suffix = ".pbstream";
+  if (state_filename.substr(
+          std::max<int>(state_filename.size() - suffix.size(), 0)) != suffix) {
+    LOG(WARNING) << "The file containing the state should be a "
+                    ".pbstream file.";
+  }
+  LOG(INFO) << "Loading saved state '" << state_filename << "'...";
+  io::ProtoStreamReader stream(state_filename);
+  return LoadState(&stream, true);
 }
 
 }  // namespace mapping
diff --git a/cartographer/mapping/map_builder.h b/cartographer/mapping/map_builder.h
index 880f3bd..8d3f847 100644
--- a/cartographer/mapping/map_builder.h
+++ b/cartographer/mapping/map_builder.h
@@ -58,8 +58,10 @@ class MapBuilder : public MapBuilderInterface {
 
   void SerializeState(io::ProtoStreamWriterInterface *writer) override;
 
-  void LoadState(io::ProtoStreamReaderInterface *reader,
-                 bool load_frozen_state) override;
+  std::map<int, int> LoadState(io::ProtoStreamReaderInterface *reader,
+                               bool load_frozen_state) override;
+
+  std::map<int, int> LoadStateFromFile(const std::string &filename) override;
 
   mapping::PoseGraphInterface *pose_graph() override {
     return pose_graph_.get();
diff --git a/cartographer/mapping/map_builder_interface.h b/cartographer/mapping/map_builder_interface.h
index 5b0cbe3..fd57fe2 100644
--- a/cartographer/mapping/map_builder_interface.h
+++ b/cartographer/mapping/map_builder_interface.h
@@ -80,9 +80,15 @@ class MapBuilderInterface {
   // Serializes the current state to a proto stream.
   virtual void SerializeState(io::ProtoStreamWriterInterface* writer) = 0;
 
-  // Loads the SLAM state from a proto stream.
-  virtual void LoadState(io::ProtoStreamReaderInterface* reader,
-                         bool load_frozen_state) = 0;
+  // Loads the SLAM state from a proto stream. Returns the remapping of new
+  // trajectory_ids.
+  virtual std::map<int /* trajectory id in proto */, int /* trajectory id */>
+  LoadState(io::ProtoStreamReaderInterface* reader, bool load_frozen_state) = 0;
+
+  // Loads the SLAM state froma a pbstream file. Returns the remapping of new
+  // trajectory_ids.
+  virtual std::map<int /* trajectory id in proto */, int /* trajectory id */>
+  LoadStateFromFile(const std::string& filename) = 0;
 
   virtual int num_trajectory_builders() const = 0;