The effect of subcutaneously injected gossypol on the estrous cycle and ovarian weights in rats was examined. Daily injections of 5 or 10 mg gossypol/kg/day for 20 days significantly reduced the ovarian weights by 32% and 29%, respectively. Injections of 0.1 and 1.0 mg gossypol/kg/day had no significant effect on ovarian weight. Similarly, ovarian weights were significantly reduced by 37% when hemi-ovariectomized animals were injected with 10 mg gossypol/kg/day for 15 days whereas those of control animals increased in weight by 15%. Animals receiving 5 or 10 mg gossypol/kg/day essentially remained in diestrus by the 15th or the 10th day of injections, respectively. No significant change was found in the liver, adrenal gland or body weight of gossypol-treated rats.