The rate of sputum conversion (continuously negative cultures for six months or more) was compared among four regimens given to 83 patients with moderately advanced, cavitary lung disease caused by Mycobacterium avium complex untreated previously. The regimens of rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin appeared to be superior to the regimen of rifampin + isoniazid + ethambutol. No statistically significant difference was observed between the regimens rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin.