Hi Sergei See my earlier post on this. The once.cpp file needs changing. Get rid of the compare_exchange() wrapper stuff and substitute InterlockedCompareExchage() calls where it is called. _InterlockedCompareExchage() is a compiler intrinsic for Windows AMD64 64-bit so you won't find it in a library. The boost developers are working on a rewrite of boost/thread (same interface as I understand it) so they are a bit quiet on thread issues at the moment. Bill Somerville On 29 Mar 2006, at 09:17, Sergei N. Malyutin wrote: Hi, I need to use boost libraries under amd64 platform. At the build time of the library boost_thread I've got an error message from the linker that it failed to find an external symbol _InterlockedCompareExchange (this call is used in the source once.cpp). I really have not found this export among system libraries functions. Does this mean that currently the boost cannot be used in this environment? I did not see any limitations on the boost use under x64. May be I missed anything? Any help or links to the required information would be appreciated. Sergei Malyutin