Hi, On my system (powerpc G3, mac os 10.3.9, GMP 4.2.1) it looks like the high bit of the output of mpz_rrandomb is always 1. i.e. if I ask for n bits, then bit #n is 1. Is this intentional? I have ended up wrapping it in another function which bit-complements the output with probability 1/2. David