This paper uses the method of conversation analysis to investigate the varying degrees of medical authority being exerted through doctors' treatment recommendations, and the extent to which patients comply or resist. The research data draws on a corpus of 70 audio recorded encounters between doctors and HIV-positive patients in clinics in Southwestern Nigeria. Analyses of the consultations suggest that discussions about patients' adherence to treatment recommendations is predominant in the routine visits of HIV-positive patients. Doctors invoke high and low degrees of medical authority when recommending treatment while patients respond by endorsing or resisting the doctors' authority. For the implications on medical practice, the findings are that doctors seldom pull back with respect to displays of authority, although patients retain the rights to take life- and health-preserving drugs.