The subjective impression among clinicians that the use of Rifater was causing delayed sputum conversion and increased drug resistance was tested in a prospective study. Adults in the Cape Town municipal area with a first episode of pulmonary tuberculosis were treated either with Rifater or a regimen consisting of isoniazid, rifampicin, pyrazinamide and ethambutol. All patients who took the treatment as prescribed (67 Rifater, 39 the 4-drug regimen) converted to a negative sputum culture by the time 90 doses had been taken. The rates of inadequate compliance and of side-effects were similar in the two groups. Drug sensitivity testing of bacteria cultured from pre-treatment sputum specimens revealed an overall primary resistance rate of 4.84% in the population studied, sufficiently low to preclude any necessity for routine pre-treatment drug sensitivity testing.