Induction of some estrus phenomena was achieved. Treatment with 25 mg prostaglandin-2.alpha. caused mucus discharge, within 48-72 h after injection, which lasted for 4-5 days. Rectal palpation indicated rapid regression of the corpus luteum, and in 9 treatments of 6 buffaloes serum progesterone levels declined from 1.76 .+-. 0.01 (s.d.) ng/ml before treatment to < 0.25 ng/ml within 24 h after injection. Concentrations increased at .apprx. day 11 and reached a peak of 1.78 .+-. 0.62 ng/ml on day 18.50 .+-. 2.45.