Two-stage pharmacokinetic studies were conducted in patients suffering from pulmonary tuberculosis treated with rifampicin (RMP). At the first stage of the studies in 100 patients blood and urinary drug levels were determined. The results showed that RMP applied orally penetrates rapidly into the circulation and reaches high serum concentrations varying largely in individual patients. At the second stage of the studies in further 30 patients blood, urinary and sputum RMP levels were simultaneously determined and the biological half-life of RMP and its distribution were checked. It was found that the biological half-life of RMP was 3.79 h, the distribution at the initial stage 38%, and after a few weeks of treatment 52.1%. The authors are of the opinion that the increased value of this parameter has a direct effect on the fall in serum RMP concentration at the later period of treatment. The amount of active RMP excreted by the kidneys of patients with lung tuberculosis averages 33.5%.