Chlordimeform [N'-(4-chloro-o-tolyl)-N,N-dimethylformamidine] has been shown to cause a 1-day delay in the surge of luteinizing hormone (LH) in ovariectomized, steroid-primed female rats, presumably through its ability to block CNS alpha-noradrenergic receptors and consequently CNS regulation of anterior pituitary function. In the present study, we determined whether a chlordimeform-induced delay in the ovulatory surge of LH would alter pregnancy outcome in intact females. Chlordimeform (50 mg/kg) or sodium pentobarbital (35 mg/kg), as a positive control, was administered in order to delay ovulation 24 (1-day delay) or 48 hr (2-day delay). Females were then housed with proven fertile males on the evening of proestrus (0-day delay group), the following evening (1-day delay group), or the evening after that (2-day delay group). The number of receptive females in each group, the mean lordosis quotient, and the number of sperm-positive females in each group were recorded. All females were killed on Gestation Day 20. The number of pregnant females in the 1- or 2-day delay groups was reduced with both chlordimeform and pentobarbital. Also, delaying ovulation for 1 or 2 days with either compound resulted in a significant reduction in the number of live pups present on Gestation Day 20 and a decrease in the number of implantation sites. Litter size was not affected if the females were mated on the same day that treatment was administered (0-day delay).(ABSTRACT TRUNCATED AT 250 WORDS)