Hi there, I couldn't find anything in the archives for my problem. Purify is showing several memory leaks when I execute the following program: int _tmain(int argc, _TCHAR* argv[]) { // prepare some data to write unsigned int nSize = 1000000; char* pBits = new char[nSize]; ::memset( pBits , 0 , nSize ); for( unsigned int i = 0; i < nSize; i++ ) { pBits[i] = i; } // write to file io::filtering_ostream out; out.push( io::zlib_compressor() ); out.push( io::file_sink( "test.zip", std::ios::binary )); out << nSize; out.write( pBits , nSize ); // clean up delete[] pBits; return 0; } I think the program is right. I'm using Boost 1.33 with VC 7.1. Here is what purify spits out: [I] Summary of all memory leaks... {268108 bytes, 6 blocks} [I] MPK: Potential memory leak of 196608 bytes from 3 blocks allocated in boost::iostreams::detail::zlib_base::do_init(zlib_params::iostreams::boost const&,bool,(*)(void *,UINT,UINT),(*)(void *,void *),void *) [IOStreams.exe] [W] MLK: Memory leak of 71360 bytes from 2 blocks allocated in boost::iostreams::detail::zlib_base::do_init(zlib_params::iostreams::boost const&,bool,(*)(void *,UINT,UINT),(*)(void *,void *),void *) [IOStreams.exe] Is that a know issue? I guess so, but has it been resolved? Thanks, Christian