During a period of 14 months in 1985 and 1986, infection with Mycobacterium aviumintracellulare (MAI) complex was diagnosed in 10 of 76 patients with Human Immunodeficiency Virus (HIV)-associated infection. In eight of the 10 patients, the infection was disseminated. All eight patients were anaemic. A bone marrow aspirate and/or trephine biopsy performed in six of them revealed evidence of red cell hypoplasia. MAI was cultured from all six samples of bone marrow. The strains of MAI isolated were resistant to conventional antituberculous drugs but were susceptible in vitro to ansamycin, ethionamide and cycloserine. None of the eight patients responded clinically to antituberculous therapy. The eight anaemic patients had pronounced constitutional symptoms. We suggest that severe anaemia and constitutional symptoms in patients with HIV-associated disease should prompt a search for evidence of disseminated MAI infection.