Electrical activity of rabbit oviducts was recorded in vitro at 18, 24, and 68 h after injection of human chorionic gonadotropin. An array of eight suction electrodes 1-2 mm apart was moved sequentially to cover nearly the whole oviduct. The frequency of spike bursts, pacemaker frequency, percentage of nonpropagating bursts, and probability of propagating in the uterine direction varied steeply within a few millimeters along the oviduct. On the average, spreading was only slightly prouterine. Compared to 18 and 24-h, 68-h oviducts showed higher frequency of activity and longer distances of propagation, particularly in the isthmus. The activity extended to 65.8 and 69.6% of the distance from the fimbriae at 18 and 24 h, respectively, and at 68 h to 70.8% and 84.6% in those oviducts that contained and did not contain ova, respectively. Ova were recovered on the uterine side of the border of activity or in regions in which the percentage of nonpropagating bursts was high or, at 18 and 24 h, in segments containing local regions of inactivity. Apparently, frequency of activity, the degree to which propagation of activity deviates from randomness, and the length of the inactive area regulate the location of ova in the isthmus.