Observations on the behavioral development of two okapi calves and one giraffe calf were made at Brookfield Zoo. The following behaviors were monitored for 4 to 6 mo after birth: nursing duration and nursing attempts, mother-infant distance, bunting the mother's udder, lying, moving, maternal grooming, mother and infant autogrooming, object licking, tail chewing, and contact by others in the herd. Behaviors in both species showed oscillating patterns with high levels of motherinfant contact behaviors at 3-4 wk, 9-11 wk, and 14-15 wk in okapis. Giraffe infants showed similar oscillations with high periods of contact about 2-5 wk later than those in okapis. Other behaviors oscillated in concert with these, with specific correlations occurring between nursing behaviors and grooming behaviors.A main difference between okapi and giraffe development centered around maternal motivation during the high contact (regressive) periods. In okapis, after 10-12 wk there was a low rate of nursing success, whereas in giraffes the percentage of success in nursing rose with later behavioral oscillations. The regressive periods became conflict periods in okapis, whereas in the giraffe, the mother initiated the periods. This difference was in accordance with the unique strategy of infant rearing in wild giraffes in which there is an extended "hider" period when older calves are left together in shaded areas with an adult sentry. Field studies also indicated probable oscillations of mother-infant contact and a prolonged period of the mother initiating contact with her calf.