Patients are randomized to receive oral rifabutin alone or rifabutin/ethambutol daily for 12 months, with possible continuation of medicine lifelong. Doses will be adjusted to maintain minimum blood levels of the drugs.

Inclusion Criteria

Concurrent Medication:

Required:

• AZT, d4T, ddI, or ddC.
• Antipneumocystis prophylaxis.

Allowed:

• Short course (< 14 days) of ciprofloxacin for acute infections.

Patients must have:

• AIDS.
• CD4 count <= 100 cells/mm3.
• NO prior or current MAC infection.

Prior Medication:

Required:

• Antipneumocystis prophylaxis for at least 4 weeks prior to study entry.

Allowed:

• Prior rifabutin.
• Prior ethambutol.
• Prior clarithromycin.

Exclusion Criteria

Co-existing Condition:

Patients with the following symptoms or conditions are excluded:

• Positive tuberculin skin test (PPD > 5 mm).
• Active M. tuberculosis.
• Perceived as unreliable or unavailable for frequent monitoring.

Concurrent Medication:

Excluded:

• Other antiretrovirals not specifically allowed.
• All investigational drugs.
• Other antimycobacterial therapy, such as clarithromycin, azithromycin, rifampin, clofazimine, amikacin, streptomycin, isoniazid, cycloserine, ethionamide, and ciprofloxacin (>= 14 days).

Patients with the following prior conditions are excluded:

Known hypersensitivity to rifabutin, rifampin, or other rifamycins and/or ethambutol.

Prior Medication:

Excluded within 4 weeks prior to study entry:

• Rifampin.
• Isoniazid.
• Clofazimine.
• Cycloserine.
• Ethionamide.
• Amikacin.
• Ciprofloxacin.