I'm working on a project with strict requirements for the build settings, including mandatory warning level 4 and "treat warnings as errors". I discovered that lexical_cast causes warnings C4127, C4511, and C4512 when compiling with warning level 4 using VC7.1. Try the following code for a quick repro: #include <string> #include <iostream> #include "boost/lexical_cast.hpp" int main() { std::string helloFactor = boost::lexical_cast<std::string>( 7 ) ; std::cout << "Hello # " << helloFactor << std::endl ; return 0 ; } Builds fine at warning level 3, fails with /W4 and /WX. As an aside, what warning level is typically used by developers working on Boost? -Bruce Johnston Simba Technologies