Removal of the eyes (Reiter, 1968) or of the olfactory bulbs (Orbach & Kling, 1966) slightly delays gonadal maturation in rats. The gonadal inhibitory effect of blinding is prevented if animals are pinealectomized (Reiter, 1968). It was found recently that if weanling male rats have both their eyes and olfactory bulbs removed, the testes are less than half their normal size at 70 days of age; this entire effect is reversed if the animals also have their pineal gland removed. This indicates that another external factor, in addition to the photo-period, may influence directly or indirectly the antigonadotrophic activity of the pineal gland. The experiment was repeated and the following data illustrate some interrelationships between olfaction, photo-period, the pineal gland and reproduction. Sixty-four 21- to 23-day-old