No difference was noted either in the time of ovulation or in the number of ova released among the four treatment groups. Also, no difference was noted in the number of pups or fetuses, number of implantation sites, or number of reabsorbed fetuses. The organ weights in pinealectomized rats were generally higher and the organ weights in melatonin-injected rats were generally lower than their respective controls only on Day 1 and the day of delivery, i.e., on the days when the animal is not, in fact, pregnant. The rise in pituitary LH content in all four treatment groups during pregnancy with no concomitant change in serum LH indicates that the rise in pituitary LH during pregnancy may represent only an increased storage of LH by the pituitary with little or no LH release. A possible explanation for the increased serum LH concentration on Days 1 and 23 in melatonin-injected animals is offered. A fourfold increase in pituitary FSH is noted by Day 16 in all four groups. The pituitary content of FSH remained high until Day 22 and fell by the day of delivery to a level equal to that on Day 1. It appears, therefore, that under "normal" laboratory conditions the role that the pineal gland plays in ovulation and pregnancy is minimal at best. The greatest effect of the pineal on the parameters measured appears to occur on Days 1 and 23, i.e., before fertilization and after delivery.