Subjective, behavioral and physiological effects of smoked marijuana were measured with a cumulative dosing procedure which allowed dose-related effects to be determined within a single experimental session. Five male and three female occasional marijuana smokers participated. Unit doses of marijuana smoke were administered in a standardized manner on four occasions during each session, each occasion spaced 20 minutes apart. This procedure resulted in a cumulative dose of active (1.4%-THC) marijuana of 0, 2, 4 and 8 puffs after the four successive smoking occasions, respectively. Dependent variables were measured after each smoking occasion. Smoke absorption was monitored by measuring expired air carbon monoxide levels. Subjects participated in three identical sessions spaced a week apart in order to assess the reliability of the procedure. During a fourth session, only placebo (0.0%-THC) marijuana was administered throughout the session as a control. Significant linear dose-effect functions were obtained on several measures, with good session-to-session replicability of most effects. The results demonstrate the feasibility of using a cumulative dosing procedure to evaluate dose-related effects of smoked marijuana in humans. The procedure would be especially useful for the assessment of shifts in dose-effect curves as a result of various experimental manipulations.