diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index bcae21bf7..2391fd9e8 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -98,7 +98,10 @@ bool RemoteStore::hasSubstitutes(const Path & path)
 
 Hash RemoteStore::queryPathHash(const Path & path)
 {
-    throw Error("not implemented 3");
+    writeInt(wopQueryPathHash, to);
+    writeString(path, to);
+    string hash = readString(from);
+    return parseHash(htSHA256, hash);
 }
 
 
diff --git a/src/nix-worker/Makefile.am b/src/nix-worker/Makefile.am
index 6f10efff5..46568e9e1 100644
--- a/src/nix-worker/Makefile.am
+++ b/src/nix-worker/Makefile.am
@@ -4,6 +4,11 @@ nix_worker_SOURCES = main.cc
 nix_worker_LDADD = ../libmain/libmain.la ../libstore/libstore.la ../libutil/libutil.la \
  ../boost/format/libformat.la ${bdb_lib} ${aterm_lib}
 
+main.o: help.txt.hh
+
+%.txt.hh: %.txt
+	../bin2c/bin2c helpText < $< > $@ || (rm $@ && exit 1)
+
 AM_CXXFLAGS = \
  -I$(srcdir)/.. ${bdb_include} $(aterm_include) -I$(srcdir)/../libutil \
  -I$(srcdir)/../libstore -I$(srcdir)/../libmain
diff --git a/src/nix-worker/help.txt b/src/nix-worker/help.txt
new file mode 100644
index 000000000..b4583cb7e
--- /dev/null
+++ b/src/nix-worker/help.txt
@@ -0,0 +1,10 @@
+Usage: nix-worker [OPTIONS...] [--daemon | --slave]
+
+`nix-worker' is a helper program used to implement secure, multi-user
+Nix stores.  In `--daemon' mode, it goes into the background and waits
+for incoming connections on a Unix domain socket, and forks a process
+for each connection to perform the Nix store operations requested by
+the caller.  In `--slave' mode, `nix-worker' is called directly, and
+the caller and the worker communicate with each other over
+stdin/stdout.  In this mode, the `nix-worker' program should have
+appropriate setuid privileges.
diff --git a/src/nix-worker/main.cc b/src/nix-worker/main.cc
index 6d6571536..95077e653 100644
--- a/src/nix-worker/main.cc
+++ b/src/nix-worker/main.cc
@@ -5,6 +5,8 @@
 #include "worker-protocol.hh"
 #include "archive.hh"
 
+#include <iostream>
+
 using namespace nix;
 
 
@@ -48,12 +50,13 @@ void processConnection(Source & from, Sink & to)
 
         switch (op) {
 
-        case wopQuit:
+        case wopQuit: {
             /* Close the database. */
             store.reset((StoreAPI *) 0);
             writeInt(1, to);
             quit = true;
             break;
+        }
 
         case wopIsValidPath: {
             Path path = readStorePath(from);
@@ -67,6 +70,12 @@ void processConnection(Source & from, Sink & to)
             break;
         }
 
+        case wopQueryPathHash: {
+            Path path = readStorePath(from);
+            writeString(printHash(store->queryPathHash(path)), to);
+            break;
+        }
+
         case wopQueryReferences:
         case wopQueryReferrers: {
             Path path = readStorePath(from);
@@ -153,8 +162,11 @@ void run(Strings args)
 }
 
 
+#include "help.txt.hh"
+
 void printHelp()
 {
+    std::cout << string((char *) helpText, sizeof helpText);
 }