The two populations, one in an early and another in an advanced stage of drug-use career, were investigated by different methods. These respondents (students and imprisoned drug dependents) showed a pattern of increased substance dependency with a wider range of substances used. Problems that affected the physical and mental health and social functioning of imprisoned drug dependents were also evident among student drug users, especially those who had used heroin. The authors conclude that the choice of the method to be used in drug-dependence research does not depend primarily on the nature and priorities of the chosen objectives; however, factors such as local situation and the availability of resources often prevail over scientific considerations. Longitudinal studies are more appropriate than cross-sectional studies to investigate causal relationships and temporal issues. Nevertheless, single-phase, cross-cultural surveys can provide a wealth of information that can effectively be used for guiding social policy and preventive initiatives. 22 references, 3 figures, and 2 tables