In two 4.5-month regimens and one 3-month regimen the four most potent antituberculous drugs (isoniazid, rifampin, pyrazinamide, and streptomycin) were given for the initial 3 months of chemotherapy. Acceptance by the patients was high, and bacillary sterilization was achieved in 96% of cases within 2 months. Addition of a fifth drug, ethionamide, during the initial 3 months was neither acceptable nor useful. No relapses were observed during a 12-month follow-up period after completion of the 4.5-month regimens. A relapse rate of 5% followed the 3-month regimen. The toxicity and side effects of antituberculous drugs were observed in 16% of patients during the initial 3-month period. In 3.4% of patients, toxicity necessitated cessation of treatment. In the remaining 13% of patients, adverse side effects could be managed without cessation of treatment. Even when patients were ambulatory and outpatient attendance was required for drug administration, the noncompliance rate was only approximately 10%. With the current over-all cost of drugs being limited to 100 United States dollars, the patients with moderately extensive disease must be treated for 100 days, or a maximum of 100 doses.