Rabbits nurse briefly only once each night and are frequently both pregnant and lactating. To investigate the influence of the daily timing of nursing on parturition, does (n = 10 per group) were remated after giving birth and were allowed to nurse under one of three schedules: group 1 every 24 h in the light, group 2 every 24 h in the dark, and group 3 at any time. Whereas does from groups 2 and 3 nursed and gave birth normally, does of group 1, forced to nurse out of phase with the normal schedule, showed disturbed nursing behavior and prolonged gestation followed by many stillbirths. In a second experiment, pregnant does (n = 10 per group) were treated daily either with oxytocin (OT) in the light (group 4), with OT in the dark (group 5), or with progesterone (P; group 6) or saline (group 7) in the light. All does gave birth normally except those of group 4, which responded similarly to group 1 does. These findings demonstrate that in the rabbit, parturition may be seriously compromised if does nurse out of phase with the normal schedule and suggest that a shift in the daily timing of OT release may underlie this.