Hi, I did some development with libboost_regex-gcc.so (1.31.0) on a Linux platform: no problems. However, when I try to compile on FreeBSD, I get the following errors: g++ -o myprog Unit1.o Unit2.o /usr/local/lib/libboost_regex-gcc.so /usr/local/lib/libboost_regex-gcc.so: undefined reference to 'pthread_mutex_unlock' /usr/local/lib/libboost_regex-gcc.so: undefined reference to 'pthread_mutex_destroy' /usr/local/lib/libboost_regex-gcc.so: undefined reference to 'pthread_mutex_lock' /usr/local/lib/libboost_regex-gcc.so: undefined reference to 'pthread_mutex_init' I've installed Boost on the FreeBSD platform using both the ports package available from freebsd.org and the source from boost.org. Both yield the same results. Any ideas appreciated, as I am not that experienced with C++, Boost, and cross-platform deployment. Thanks, Steve