Cerebral blood flow (CBF) was measured in experienced (ES) and inexperienced (IS) marijuana smokers with the 133xenon inhalation technique before and after smoking both a high-potency marijuana cigarette and a placebo marijuana cigarette. CBF was measured twice under resting conditions in a control group. Mood states before and after marijuana smoking were quantified with the Profile of Mood States (POMS). Analyses of POMS factors after smoking marijuana revealed IS had an increase in anxiety while ES had a decrease. IS also had a significant increase in depression and decrease in vigor, but neither variable changed in the ES. After marijuana, CBF decreased in IS, but in ES, it increased in comparison with the 2 control runs. In both IS and ES, CBF changes following placebo administration were similar to those associated with marijuana smoking. However, in IS, the marijuana-induced CBF decrease was significantly higher than that associated with placebo. There were no statistically significant differences between the CBF increase seen after placebo and marijuana in ES. Anxiety, anger, fatigue, confusion and depression had significant negative correlations with CBF while vigor correlated positively, but the anxiety factor was the only one to account for a significant percentage of the change (parital correlation) in hemispheric CBF.