The ultrastruetural changes of the cells of adenohypophysis were observed in adult male rats following administration of gossypol at a daily dosage of 30 mg/kg for 5 weeks. The results indicated a remarkable increase in the secretory activity of gonadotrophs. In comparison with the control group, the number of the less actively functioning types Ⅰ and Ⅱ gonadotrophs of gossypol-treated rats decreased, while that of types Ⅲ and Ⅳ cells with developed Golgi complex and dilated rough endoplasmic reticulum increased. Moreover, castration-like cells (type Ⅴ) and degranulation cells (type Ⅵ) appeared in the experimental animals. No significant changes in the other tropic cells of adenohypophysis could be found. The classification of gonadotrophs and the possible mechanism of gossypol-induced changes in them are discussed.