The prevalence and pattern of substance use was investigated among undergraduate students of the University of Ilorin, Kwara State, Nigeria in June 1988. Six hundred and forty-nine students completed a 117-item self-report questionnaire 636 of which were analysed. Mean age and S.D. of respondents was 23 +/- 3.7 years; 69% were males. The most commonly used substances with their 'lifetime' prevalence rates were as follows: salicylate analgesics, 95.2%; alcohol, 77%; stimulants, 69.2%; antibiotics, 63.3%; hypno-sedatives, 49.4% and cigarettes, 37.4%. The corresponding 'current use' rates were relatively lower. Low use was recorded for cannabis, organic solvents, hallucinogens, cocaine and narcotic analgesics. Majority of the 'current users' use the substances on an occasional basis except for cigarettes where more than half reported weekly or daily use. Males were significantly more of 'current' users of cigarettes and alcohol while females tend to use stimulants more. The use of most of the substances started in primary school. The need for a comprehensive demand-reduction programme in Nigeria based on this and other local findings was advocated. Continuous monitoring, particularly of hard drug use, appears imperative.