AbstractInjecting practices of illicit drug users in San Antonio, Texas, were studied by means of informal field interviews and participant observation. The methods injection drug users (IDUs) employed to obtain drugs seemed to affect their HIV risk behaviors. Many of the methods involve reciprocal exchanges between a person who has drugs and a person who wants drugs. The exchanges frequently occur in the context of asymmetrical social interactions. The person with the drugs usually occupies the dominant role in the interaction and determines the needle hygiene for both parties. Analysis of the decision-making process of IDUs indicates that the party in the dominant role may choose not to disinfect a syringe for a variety of reasons. An understanding of the subcultural rules that govern these interactions may provide valuable clues to researchers or educators who are designing interventions aimed at reducing HIV risk behaviors among IDUs. This research suggests that for IDUs in subordinate roles, education alone may be insufficient to produce behavior changes necessary to eliminate risk of HIV infection.