A substantial majority of the 60 drug users interviewed for this study cited the widespread popularity of illegal drugs during the late 1960s and early 1970s in this country's youth movement and in Vietnam as the major factor in initial drug use. This explanation is consistent with the typical sociological emphasis on social and subcultural factors. However, after the respondents' drug use expanded to include heroin, their motivations changed dramatically. Sooner or later physiological survival needs displaced social motives as the main reason for continued drug use. Although clients continued to participate in the drug subculture as a matter of necessity, their conscious motivation was physical survival, not social rewards. This emphasis on physiological needs is consistent with the medical perspective of the clinic, and the clinic environment may help to reinforce it in clients' minds. Footnotes, references