The effect of angiotensin II (Ang II) on the follicular development was studied by using an animal model of follicular atresia induced by pregnant mare s serum gonadotropin (PMSG). The results showed that: (1) a large number of atretic follicles were found in the ovary of 24-day-old mouse after 6-day treatment of PMSG. Deoxyribonucleic acid (DNA) extracted from granulosa cells clearly showed a ladder band under agarose gel electrophoresis analysis. (2) the contents of Ang II in the ovary extremely increased with the development of follicular atresia. (3) Ang II significantly antagonized the stimulating effect of the follicle-stimulating hormone (FSH) on estradiol (E(2)) generation of granulosa cells. It is suggested that Ang II may be involved in the regulation of follicular atresia in mouse.