Mycobacterium avium complex infections, common in patients with AIDS as either pulmonary or disseminated disease, are infrequent in patients without AIDS. Participants were 45 HIV-negative patients with lung disease and positive sputum cultures for M avium; 10 had documented immunocompromise, and 24 had preexisting lung disease, Clarithromycin dosage was 500 to 2,000 mg daily (mean+/-SD=1,633+/-432 mg), The drug was administered either alone (n=14) or in combination with rifampin (n=8), aminoglycoside (n=1), quinolone (n=10), clofazimine (n=18), isoniazid (n=5), ethambutol (n=9), pyrazinamide (n=1), or minocycline (n=6). At 3 months, 36 patients among 39 bacteriologically assessed had negative sputum cultures, 3 had positive culture, 3 were dead, and 3 discontinued treatment. At the end of treatment, 32 patients remained negative, 7 were positive. The success rate was 15 of 22 (64%) in patients previously treated with antimycobacterial drugs for M avium disease and 17 of 23 (74%) in new patients, Adverse effects included mild hearing loss (n=4), increase in liver enzyme levels (n=5), and gastrointestinal pain (n=10, two of whom had to stop treatment), Patients stopped treatment after 300+/-186 days due to side effects (3), death (4), or the patient's (5) or physician's decision (33), During the follow-up, one patient suffered a relapse with peripheral lymph nodes. A daily dose of 30 mg/kg of clarithromycin in the treatment of M avium infections appears to be effective and safe, Concomitant drug therapy should be assessed for its ability to prevent relapse.