Squirrel monkeys were trained to press either two (phase one) or five (phase two) differently colored keys sequentially. Food presentation resulted if colors were pressed in a specific order, and high levels or accuracy were generated. Acutely, delta 9-tetrahydrocannabinol reduced accuracy and rate of responding in a dose-related fashion under both the two-key and five-key conditions. Responding, however, was more sensitive to the drug under the five-key procedure. Accuracy of responding at the beginning of a sequence tended to be more sensitive to drug effects than responding near the end. Daily (chronic) administration resulted in the development of tolerance to both the rate- and accuracy-reducing effects of the drug, although tolerance developed more rapidly to the accuracy-reducing effects. Tolerance developed more slowly under the five-key procedure than under the two-key procedure. Details of tolerance development were related to aspects of acute effects, suggesting that some facets of tolerance development may be predictable from acute drug effects.