One hundred nineteen patients 15 to 70 yr of age, all with smear-positive, previously untreated, pulmonary tuberculosis, were treated with a 6-month regimen containing isoniazid and rifampin, supplemented during the initial 2 months with streptomycin and pyrazinamide. The 4 drugs were administered daily in the hospital during the initial 2 months, followed by isoniazid and rifampin administered twice weekly on an outpatient basis during the next 4 months. Adverse reactions to the drugs were seen in 19 patients, but only 6 had toxic reactions requiring withdrawal of drugs for 7 days or more. Three of the toxic reactions were attributed to streptomycin, 2 to rifampin, 1 to isoniazid, and none to pyrazinamide. Eighty-five (71%) of the 119 eligible patients completed treatment. After the first 2 months of therapy, 91% of these patients had negative sputum cultures, and all of them had negative cultures by the end of the third month of treatment. No relapses have occurred among the 84 patients observed for 18 months after therapy was completed.