In the drug field the fundamental epidemiological question-why illicit drug use, here, now, among these people-has still not been adequately answered. Drawing on the work of colleagues in medical anthropology, we attempt to move closer to an answer by developing a "trend theory." In this article we analyze a single case: the increase in heroin use and addiction among African Americans in the City of Baltimore in the 1960s. We found that the two most important historical processes behind the epidemic were (1) a changing distribution/supply system and (2) the mix of hope and despair that was part of the early civil rights movement.