A total of 112 volunteer males, aged 18-30 years, were randomly assigned to eight groups, with 14 subjects per group. For each of two drug conditions (no drug and marihuana), there were four motivation conditions. In the first motivation group, the subjects were merely given instructions concerning how to perform on each dependent measure. The second motivation group was given the additional instructions to "try as hard as possible" on each measure. The third motivation group could earn a small amount of money, contingent on the performance of the dependent measures. The fourth group could earn a substantial amount of money contingent upon task performance. Time perception, choice reaction time, and a paired-associate memory task were used as dependent measures. The results indicated a significant, detrimental drug effect on all measures and a significant motivation effect on the reaction time measure. Close examination of the data suggests that the drug effect occurred because of the ineffectiveness of the motivation manipulation with the marihuana subjects.Much diversity of opinion surrounds the phenomenon of marihuana intoxication. There is presently little agreement among researchers on the effect of marihuana on behavior. For example, whereas some authors have found that marihuana impairs various coordination and cognitive skills (reviewed in LeDain, Campbell, Lehmann, Stein, & Bertrand, 1972) others have suggested that attentional factors and boredom might be producing these deficits (e.g., Manno, Kiplinger, Scholz, & Forney, 1971). Indeed, there is an increasing body of evidence to support the notion that extrapharmacological factors may play at least as great a role in marihuana intoxication as the drug itself.