Patients receive both clarithromycin and ethambutol for 48 weeks; those who become intolerant to the study drugs may receive suggested substitute drugs (azithromycin and rifabutin). Patients receive a bone marrow biopsy at baseline and at either 4 or 8 weeks. Patients are evaluated at weeks 1, 2, 4, 6, 8, 12, 24, 36, and 48.