Partial conductivity-type conversion has been observed in monocrystalline p-type CuInSe2 samples after heat treatment in argon at atmospheric pressure at a temperature of 500 degrees C. The hole concentration in the samples at room temperature was about 10(17) cm(-3). The depth of the outer converted n layer in the original p-type material, as determined by hot probing and etching, increased approximately as the square root of the annealing time. This variation suggested an outdiffusing acceptor with a diffusion coefficient at 500 degrees C of about 7.3x10(-7) cm(2) s(-1) and a compensation donor/acceptor concentration ratio in the original p-type material of less than 10%. Auger profiles recorded on similar stoichiometrically prepared monocrystals, after annealing at 350 degrees C for 2 h, indicated a 2%-4% loss of Se, thus identifying this element as the main outdiffusing agent.