The authors investigated the influence of associative pairing of contextual stimuli with amphetamine administration on the expression of psychomotor sensitization. Animals received d-amphetamine or saline in group-specific environments. Amphetamine produced robust behavioral sensitization in all environments, but when an amphetamine challenge was given in a test environment that was novel for some groups but not others, the expression of sensitization was completely context specific. An injection of saline in the amphetamine-paired environment produced a conditional response (CR), but this was quite small compared to the magnitude of the sensitized response, and sensitization remained completely context specific following extinction of the CR. Results are discussed in relation to 3 models of how context may modulate the expression of sensitization: an excitatory conditioning model, an inhibitory conditioning model, and an occasion-setting model.