In monocrystalline p-type CuInSe2 samples, with a room temperature hole concentration of approximately 10(17) cm(-3), partial type-conversion was observed to take place after heat-treatment at 500 degrees C in argon at atmospheric pressure. The depth of the outer n-layer in the original p-type material, as determined by hot probing and etching, increased opproximately as the square root of the annealing time. This variation suggested an outdiffusing acceptor with a diffusion coefficient at 500 degrees C of about 7.3 x 10(-7) cm(2)/s and a, compensation donor/acceptor concentration ratio in the original p-type material of less than 10%. Anger profiles recorded on similar stoichiometrically-prepared monocrystals indicated a 2-4% loss of Se after annealing at 350 degrees C for 2 h, thus identifying this element as the main outdiffusing agent.