Patients are randomized to one of three treatment arms containing clarithromycin in combination with ethambutol, rifabutin, or both. Clarithromycin alone is taken on days 1 through 3 to determine tolerance and rifabutin and/or ethambutol is added on day 3. AS PER AMENDMENT 7/2/97: Patients may elect to add ritonavir or indinavir to their treatment regimen. Treatment continues daily for 48 weeks. In the absence of a dose-limiting toxicity, those patients who are determined to be complete or partial responders continue on the regimen to which they were originally assigned. Patients who have failed or relapsed on originally assigned MAC therapy, must have their therapy amended to receive clarithromycin and at least two other drugs not included in their originally assigned regimen. Patients are followed twice in the first week, then every 2 weeks for the first 2 months, then monthly for the next 4 months, and then every 2 months thereafter until the end of 12 months. PER AMENDMENT 10/10/96: NOTE: Any patient who develops a toxicity to rifabutin or ethambutol after week 12 or thereafter will be offered the option of being registered to a salvage regimen of 2 new drugs not previously received, plus clarithromycin to continue for the study duration.