Illicit drug taking, particularly by young people, has increased substantially in recent years. Cannabis offences increased from 51 in 1957 to 4,683 in 1969, and offences involving amphetamines and LSD increased from 1,216 in 1966 to 3,762 in 1969. Most drug taking is undetected by the police, and is hence underestimated by conviction rates. Weiner (1969) found by questionnaire an incidence of drug-taking by London schoolchildren of 5·39 per cent, and Webb (1969) found an incidence of 24 per cent on a university campus.