The length of the oestrous cycle and plasma progesterone concentration in Ethiopian Highland zebu cows were monitored after treatment with prostaglandin F2α (PGF) (25 mg Lutalyse®) 12 days after spontaneous oestrus. PGF induced luteolysis followed by a significant drop in progesterone values to proportionately 0·11, 0·04 and 0·03 of the pre-treatment values (range 6·3 to 11·4 μg/l) within 24, 48 and 72 h of PGF injection, respectively (P < 0·001). PGF treatment resulted in oestrus within 72 to 120 h and did not influence the length of the subsequent oestrous cycle (P > 0·05). Mean oestrous cycle length was 19·4 (s.d. 1·3) days. There was good correlation (r = 0·72) between the length of consecutive cycles in the same cow and the amount of progesterone the cow produced on the same day in the cycles (r = 0·69 to 0·95). As a result, a close relationship (r = 0·74) existed in the total amount of progesterone produced in consecutive cycles. These data suggest that events following PGF treatment in Ethiopian Highland zebu cows closely parallel those observed in natural cycles. Two-thirds of the spontaneous heats exhibited elevated progesterone values 2 days prior to oestrus onset.