Beige mice were challenged with 10(6)-10(7) cfu of Mycobacterium avium intracellulare strain 101 and 22 days later treated with streptomycin 150 mg/kg/day alone, clofazimine 20 mg/kg/day alone, streptomycin 150 mg/kg/day plus clofazimine 20 mg/kg/day, or no antimicrobial agent (untreated controls). Both single-drug therapies partially reduced the cfu counts in spleen, liver and lungs compared with the controls however the combination was significantly more effective and completely eliminated the pathogen from the spleen and lungs of some animals after eight weeks treatment.