on this hot topic. <perl.h> does not seem nor does it claim to be thread safe! You will have to use ONE interpreter coupled with a mutex and throw C enywhere in between. I repeat- perl.h is not thread-safe (hell, it doesn't even provide a basic model for the beginnings of thread-safeness) and thus you are left with ONE interpreter and a mutex. Sorry to burst your bubble. This is specific to Perl as of 5.005. If you believe this NOT to be the case, please respond since this situation interests me, too, but I don't think that the