We conducted a randomized, open-label trial in 42 French hospitals to compare the clinical and bacteriologic efficacy of combination therapy with clarithromycin/clofazimine (Clm/Clof) with that of combination therapy with clarithromycin/rifabutin/ethambutol (Clm/Rib/Eth) as treatment for Mycobacterium avium bacteremia. One hundred forty-four human immunodeficiency virus-seropositive patients older than 18 years of age who had CD4 lymphocyte counts of <100/mm3 and a blood culture positive for M. avium were enrolled in the study. The main measures of outcome were blood cultures, abatement of clinical symptoms (fever), and survival. Treatment success (defined as patient living, either no fever or a reduction of > or = 1 degrees C in initial body temperature, and a blood culture negative for M. avium) was similar in both treatment groups at months 2 and 6. However, following initial resolution of infection, relapse of M. avium bacteremia occurred in more patients in the Clm/Clof group than in the Clm/Rib/Eth group (22 vs. six, respectively; P < .001); these relapses were accompanied by emergence of strains resistant to clarithromycin in 21 and two patients, respectively. In conclusion, combination therapy with Clm/Rib/Eth prevented relapse of mycobacterial disease and, compared with combination therapy with Clm/Clof, was associated with a significant decrease in the emergence of resistant M. avium strains in HIV-infected patients treated for at least 28 weeks.