Psychological tests measuring intelligence, memory and other cognitive functions were given to 26 heavy cannabis users (mean duration of cannabis use 6.76 years; average daily intake 150 mg THC). Compared with a control group, the cannabis users were found to react slowly in perceptuo-motor tasks, but not to differ in intelligence or memory tests. The users suffered disability in personal, social and vocational areas and indicated higher psychoticism and neuroticism scores.