The paper reports on a trial with Rifampicin (RMP,) used for 3 ½ years to treat a total of 250 patients. 202 of these patients could be followed up for periods of up to 42 months after discharge from the hospital. The negative findings achieved during inpatient treatment persisted throughout the whole period of follow-up observation. The radiological regression was also maintained, with increasing scar formation. In one case, a cavity transformed into a cyst was invaded by an aspergilloma 18 months after the patient’s discharge from hospital. With regard to tolerance, the trial of RMP gave favourable results. Tests did not show that RMP caused any greater increase in transaminases and bilirubin than other tuberculostatic agents. Liver biopsies were also done and showed no evidence of obvious hepatic damage at the beginning or later on in the course of treatment. It is possible that during its elimination from the liver RMP is in competition with bilirubin. Because of these precautions are indicated if the drug is given to patients with previous hepatic impairment, and above all chronic alcoholics, so that they, too, may benefit from highly tuberculostatic activity of the drug. RMP cannot be said to have any particularly toxic effect on the liv