Two groups of 10 male rats were trained to nose poke for food pellets at four alternatives that provided differing rates of pellet delivery on aperiodic schedules. After a fixed number of pellets had been delivered, 5, 10 or 20 in different conditions of the experiment, a 10-s blackout occurred, and the locations of the differing rates of pellet delivery were randomized for the next component. Two groups of rats were used: The AD group consisted of 10 rats born to dams that had normal ("ad libitum") nutrition during pregnancy, whereas the 10 rats in the UN group were from dams exposed to reduced food availability during pregnancy. All pups received normal nutrition after birth. Choice between the nose-poke alternatives quickly adapted when the rates of pellet delivery were changed in both groups, but there were no consistent differences in the speed of adaptation between the two groups. The generalized matching relation failed to describe the allocation of responses among alternatives, but the contingency-discriminability model provided a precise description of performance. (Contains 1 table and 6 figures.)