A pharmacokinetic study was carried out in 18 male patients in order to assess the blood concentrations of rifampicin after intravenous administration of 3 different doses (600, 900 and 1200 mg) over 3 different periods of infusion (1, 2 and 3 hours). The results show that, by increasing the dose and the rate of infusion higher and earlier peak concentrations are obtained. A kinetic analysis based on a one-compartment open model gives a good fitting of the data obtained experimentally. From these data one obtains for the volume of distribution a value of 48.1 +/- 17.2 liters and for the serum disappearance rate the value of 0.212 +/- 0.070 h-1 in adult subjects. It is possible to predict the time course of serum kinetics of the drug by using the equation (formula; see text).