A comparison was made between 6-month and 9-month regimens of streptomycin plus isoniazid plus pyrazinamide given daily, 3 times a week, or twice a week in the treatment of newly diagnosed, smear-positive pulmonary tuberculosis in Chinese patients. At 6 months, the twice-weekly regimen was marginally inferior; treatment failed for 5 (4 per cent) of 126 patients with drug-susceptible strains before treatment compared with 2 (1 per cent) of 141 on the 3-times-weekly regimen and none of 137 on the daily regimen. The results for patients with pretreatment strains resistant to isoniazid, to streptomycin, or to both drugs were not as good, treatment failing for 10 (30 per cent) of 33 on the daily regimen, 15 (37 per cent) of 41 on the 3-times-weekly regimen, and 14 (39 per cent) of 36 on the twice-weekly regimen. In contrast, the relapse rates after chemotherapy were similar for patients with drug-susceptible and drug-resistance strains before treatment and for patients on the daily and intermittent regimens. By 30 months, 35 (21 per cent) of 167 patients with susceptible strains who were treated for 6 months and 10 (6 per cent) of 179 treated for 9 months had relapsed, all with strains still susceptible to isoniazid and streptomycin. The relapse rates for patients with resistant strains were 7 (24 per cent) of 29 and 1 (4 per cent) of 26, respectively. Drug toxicity was not a special problem.