The olfactory bulbs were removed in 2- to 3-month-old virgin Wistar rats; one month later, the animals were tested for precocious and oestrous mating activity during 5-day cycles. The mating frequencies observed in control and operated animals, respectively, were 35/87 and 4/50 during the night following day 3 (dioestrus 3), 36/42 and 31/38 during the night following day 4 (prooestrus), and 42/70 and 17/30 during the night following day 3, following injection of a single dose of 10 µg oestradiol. Precocious ovulation was triggered by coitus in unoperated as well as in operated oestradiol-primed animals. In operated animals, no disturbance of spontaneous ovulation frequencies was recorded, but a small decrease in the mean number of corpora lutea was observed.