Previous reports from the Tuberculosis Chemotherapy Centre, Madras, have established that ambulatory treatment of pulmonary tuberculosis with the combination of isoniazid and PAS, administered daily, yields satisfactory results. However, in the usage of any unsupervised regimen, reliance must be placed on the co-operation of patients in self-administering their drugs. Irregularities in drug-taking, which are not uncommon, may lead to unfavourable therapeutic results; this might be avoided by supervised administration of the drugs. Daily supervision is clearly impracticable in developing countries but regimens in which the drug is administered intermittently-say, twice a week or less frequently-are, if effective, more likely to gain general application.This paper presents the results of a controlled study of a fully supervised intermittent regimen of isoniazid (12.5-16.1 mg/kg body-weight, orally) plus streptomycin (injected in a uniform dose of 1 g), given together twice weekly, compared with a standard, unsupervised, daily, oral regimen of isoniazid (3.7-6.3 mg/kg body-weight) plus sodium PAS (0.2-0.3 g/kg body-weight), given in two doses. The intermittent regimen was at least as effective as the standard oral regimen, and although the incidence of temporary giddiness in patients receiving this regimen was rather high, this did not appear to have any long-term importance nor did it appear unduly to affect the co-operation of the patients. These encouraging findings suggest a possible change in the orientation of drug-administration for tuberculosis in developing countries.