The male antifertility agent Gossypol did not affect the level of traditional chromosome breakage or number of micronuclei in 66-hour lymphocyte cultures at concentrations up to 40 micrograms/ml. It did increase the frequency of SCE slightly, although the inter-individual variation was greater than the increase resulting from Gossypol, and, even at the highest concentration (40 micrograms/ml), the SCE rate was still within the normal range. It also affected cell kinetics, reducing the mitotic index and the proportion of second and third metaphases after BUdR incorporation.