Such quantification depends on the application of uniform criteria and procedures that are not elaborated in this commentary due to lack of space. Much scientific work is required to delineate such career characteristics, so that comparable and reproducible recording procedures may be adopted in different countries to produce comparable information. Those who seek to conduct such comparative epidemiological studies should attempt to describe user careers with the highest degree of precision. Such workers should be encouraged to develop widely and internationally acceptable criteria and methods. The magnitude of the problem of drug abuse can be assessed through quantification, not only of the number of abusers, but also by assessment of the severity of dependence. The use of a common terminology and standard descriptions of substance abuse careers are indispensable if one hopes to compare levels of drug abuse in different countries. 14 references