Three groups of rats were trained to traverse a runway under conditions of 33% reinforcement. Two of the groups were regularly reinforced. One of the regular groups was both reinforced and nonreinforced in a gray goal box; the other was reinforced in a white goal box and nonreinforced in a white and in a black goal box. The third group was irregularly reinforced in a gray goal box. As predicted, the regular groups ran slowly following reinforcement and rapidly on the succeeding two trials. The regular gray group was transferred to a single alternation (SA) pattern of reinforcement. Immediate and consistent SA pattern running occurred. Color of goal box did not appear to be a factor in giving rise to distinctive aftereffects. It is suggested that certain of the results cannot be accounted for by a serial patterning version of the discrimination hypothesis.