Acute administration of d-amphetamine results in animals perseverating between two compartments when placed in a free running Y-maze exploratory situation. Experiment 1 indicated that perseverative behavior was attenuated by making the arms of the maze distinctively different. Experiments 2 and 3 demonstrated that repeated amphetamine treatment reduced arms of the maze distinctively different. Exeriment 2 and 3 demonstrated that repeated amphetamine treatment reduced stimulus perseveration. Drug-induced locomotor activity and stereotypy were not affected by chronic drug administration. The course of the tolerance effect was not altered by pairing the repeated drug experience with Y-maze exposure. It was concluded that although stimulus factors are involved in the perseverative response, conditioning factors are not of primary relevance in determining the tolerance. It was also suggested that the mechanisms which subserve stimulus perseveration are different from those which mediate locomotor activity and stereotypy.