Treatment of tuberculosis should be as short and as simple as possible in order to improve patient compliance; and combinations of at least three drugs should be used in order to kill the different populations of mycobacteria and to avoid development of drug resistance.--In a controlled multicentre study two regimens were compared in 93 patients with newly-diagnosed pulmonary tuberculosis: 1) Six-month therapy (47 cases): Daily rifampicin and isoniazid, supplemented with pyrazinamide for the first 2 months. A tablet with a fixed combination of 120 mg rifampicin, 50 mg isoniazid and 300 mg pyrazinamide (Rifater) was used. 2) Present Swiss standard therapy (46 cases): Daily rifampicin, isoniazid and ethambutol for 2 months followed by rifampicin and isoniazid for 7 months.--The time-course of culture negativation and the frequency of adverse events were similar in the two groups. During a follow-up period of at least two years only one relapse was observed in the six-month regimen, 3 months after completion of treatment. This was one of three patients with pretreatment resistance to isoniazid. Nevertheless, two of them were cured with the six-month regimen containing Rifater.--Patient compliance, assessed during outpatient treatment by detecting isoniazid metabolites in the urine, was very good (93% of tests were positive in each group).--These results with a follow-up of more than 2 years, indicate that short-course therapy of 6 months duration with the fixed combination tablet may be recommended as treatment of choice in pulmonary tuberculosis except in cases of isoniazid resistance and other special situations (i.e. large cavitations, large number of viable bacilli).