Groups of five pregnant bitches were treated to terminate the pregnancy with four combinations of drugs, starting 28 days after the estimated surge of luteinising hormone (LH), 22 to 28 days after the first mating. The treatments were: cabergoline administered orally for 10 days at a dose of 5 μg/kg and a single subcutaneous injection of 2.5 μg/kg cloprostenol at the start of the treatment; the same dose of cabergoline plus two doses of 1 μg/kg cloprostenol administered on days 28 and 32 after the LH surge; bromocryptine administered orally at a dose of 30 μg/kg three times a day for 10 days plus a single dose of 2.5 μg/kg cloprostenol; the same dose of bromocryptine plus two doses of 1 μg/kg cloprostenol; and a group of five pregnant bitches was left untreated. The pregnancies were terminated in all but one of the treated bitches, in each case by resorption of the fetuses. There were few side effects in the bitches treated with two doses of 1 μg/kg cloprostenol, and were present but acceptable in those treated with one dose of 2.5 μg/kg. Plasma progesterone concentrations decreased to less than 1 ng/ml within 72 hours of the start of treatment and remained low except in the bitch in which pregnancy was not terminated. In the five untreated bitches, plasma progesterone remained high and they whelped normally. In the treated groups, the intervals between successive displays of oestrus were reduced by approximately 70 days in comparison with previous cycles or with the control group, but the fertility of the dogs was not affected adversely.