I found this article from 2003. http://lists.boost.org/Archives/boost/2003/02/44515.php I gather that 9 years later, Boost.Test is still not thread-safe (at least it's still on the To-Do list). Can somebody explain what BOOST_TEST_THREAD_SAFE accomplishes? Thanks, Eric T This message, and the documents attached hereto, is intended only for the addressee and may contain privileged or confidential information. Any unauthorized disclosure is strictly prohibited. If you have received this message in error, please notify us immediately so that we may correct our internal records. Please then delete the original message. Thank you.