On Day 215 of gestation, cows were treated as controls (Group 1), bilaterally ovariectomized (Group 2), bilaterally adrenalectomized (Group 3) or bilaterally adrenalectomized and ovariectomized (Group 4). The mean +/- s.e.m. lengths of gestation (days) were 278 +/- 3 (N = 5), 270 +/- 2 (N = 7), 277 +/- 1 (N = 5) and 219 +/- 1 (N = 3) in Groups 1, 2, 3 and 4 respectively. In Group 4, serum progesterone concentrations declined to undetectable levels within 24 h after surgery and all the cows aborted 3-6 days later. All the cows in Groups 1, 2 and 3, except 1 cow in Group 2, completed gestation and delivered live calves. Progesterone concentrations in Group 2, cows declined to approximately one-third those of cows in Groups 1 or 3. All 3 cows in Group 4 and 7/8 in Group 2 had a retained placenta. At 1 and 2 days after surgery there were no significant differences in plasma levels of oestradiol-17 beta, but by the third day this difference was significant (P less than 0.01). Oestrogen levels were high before parturition in cows in Groups 1 and 3 but were not noticeably elevated in those in Groups 2 and 4. The abrupt termination of pregnancy and negligible concentrations of progesterone in adrenalectomized-ovariectomized cows indicate that the bovine adrenals contribute to progesterone production and are capable of maintaining pregnancy after ovariectomy at 215 days of gestation.