Success of antibacterial therapy depends on many factors, among which the level reached at the site of infection is important. Drug concentration in tissues and body fluids can be related to the mode of administration. The aim of the present work was to study the levels of cephotaxime (CFX) in bile, after intravenous administration of 1 g by bolus, drip infusion and bolus plus drip infusion. The drug was detected by a microbiological method. The results indicate that passage of CFX from blood into bile is a carrier-mediated process, and bolus, in the case of CFX, is the best mode of administration.