Note from Dr. Merle A. Sande--The role of Mycobacterium avium as a pathogen in the human immunodeficiency virus-infected population has been confusing and controversial to clinicians who care for AIDS patients. The organism is commonly isolated from respiratory secretions of patients with other infections and often seems part of the resident flora; even when isolated from the bone marrow or bloodstream, its impact on the course of AIDS and contribution to systemic diseases are unknown. However, an increasing subset of patients without other documented opportunistic infections or malignancies has symptoms that respond to therapy directed against M. avium. Studies are in progress to evaluate chemotherapeutic agents. Accordingly, the subject is here reviewed and guidelines offered to infectious disease clinicians by one with a long-standing interest in mycobacterial disease who has made numerous contributions to the field.