The present paper reports on an epidemiological study of the nonmedical use of psychoactive substances among male secondary school students in Greater Cairo. A standardized questionnaire was administered to 5530 male pupils constituting a representative sample of all male students in Cairo secondary schools. The main aim of the study was to provide factual answers to questions pertaining to, (a) the extent of the use of psychoactive drugs, and (b) the aetiology of such use, among secondary school students. Methodological steps undertaken to provide for representativeness of the sample and credibility of the tool are described. Among the interesting results were the following: (1) consistently more arts students than pupils reading science and maths were immersed in the drug culture; (2) sizable numbers of young people get exposed to the drug culture through well defined psychosocial channels; (3) the role of mass media in effecting this exposure seems to be quite serious, ranking in most cases after the role of personal friends; (4) a differentiation between "activists" and "passivists" among subjects who "ever used" drugs seems to be important in understanding more about drug use phenomena, and (5) some findings add a new dimension to the operational definition of high risk groups: a subgroup of nonusers could be labeled "potential users".