Termination of pregnancy in cows was investigated using sham-operated (SH) or ovariectomized (OV) cows treated with either a saline vehicle (V), cloprostenol (PG), dexamethasone (DEX) or dexamethasone and cloprostenol (DEX+PG). Surgery was done at 210 days of pregnancy and treatment was administered 72 hours later. Days (mean+/-S.E.) from treatment to termination of pregnancy for the treatment groups were: sham-operated +vehicle (SH+V): 61.5+/-11.3; ovariectomized+vehicle (OV+V): 53.4+/-15.7; sham-operated+cloprostenol (SH+PG): 61.8+/-1.7; ovariectomized+cloprostenol (OV+PG): 54.5+/-13.1; shamoperated+dexamethasone (SH+DEX): 74.8+/-4.8; ovariectomized+dexamethasone (OV+DEX): 2.8+/-0.4; shamoperated+dexamethasone+cloprostenol (SH+DEX+PG) 26.0+/-23.0; ovariectomized+dexamethasone+cloprostenol (OV+DEX+PG): 7.2+/-4.9. Pregnancies in the OV+DEX and OV+DEX+PG groups were terminated significantly earlier than in all other groups (P<0.05) except the SH+DEX+PG group. These findings suggest that dexamethasone will terminate pregnancy in cows near seven months of gestation after the ovarian source of progesterone has been removed by either an injection of prostaglandin or by ovariectomy.