Of 1072 Chinese patients with radiographically active pulmonary tuberculosis and no microscopic evidence of acid-fast bacilli in sputum examinations, only 691 (64%) were sputum-culture negative. All patients were randomly allocated to selective chemotherapy (antituberculosis chemotherapy not being started until the activity of the disease had been confirmed), to daily streptomycin, isoniazid, rifampicin, and pyrazinamide for 2 months or 3 months, or to a standard 12-month control regimen. During the subsequent 12 months, 64% of the patients in the selective chemotherapy series started antituberculosis chemotherapy. Both 2-month and 3-month regimens were inadequate for patients whose pretreatment sputum cultures were positive (relapse-rates 14% and 7%, respectively, in patients with drug-sensitive strains) but in the patients whose first cultures were negative the relapse-rate was only 1% after both short-term regimens.