Ethnographic immersion among homeless heroin addicts in San Francisco documents far more risky practices than the public health literature routinely reports. The logics of street-based income-generating strategies and the moral economy of social networking among self-identified "dope fiends" results in almost daily shares of drug preparation paraphernalia. Public health researchers need to reconceptualize their psychological behaviorist paradigm of "individual health risk behavior" because the pragmatics of income-generating strategies and the social symbolic hierarchies of respect, identity, and mutual dependence shape risky behavior. The explanatory potentials and the applied interventions that participant-observation anthropological approaches could bring to epidemiological public health research have not been utilized effectively in the field of HIV prevention and substance use. The accuracy of quantitative public health databases and our understanding of the who/why/how/where of HIV infection could be improved by a cross-methodological dialogue with participant-observation fieldworkers and by a greater theoretical sophistication with respect to power, violence, and extreme social marginalization.