The pharmacokinetics of (6R,7R)-7-[(R)-2-amino-2-(p-hydroxyphenyl)-acetamido]-3-methyl-8-oxo-5-thia-1- azabicyclo-[4,2,0]-oct-2-ene-carbonic acid (cefadroxil) were studied in rabbits with normal renal function and with varying degrees of renal impairment induced experimentally by i.v. administration of uranyl nitrate at a dose of 4 mg/kg. All animals received a single oral dose of 50 mg/kg of cefadroxil. The serum, urinary and bile concentrations of the antibiotic were determined by a microbiological method. The antibiotic follows a single-compartment kinetic model. In rabbits with renal impairment a significant decrease in Ka and Ke occurred together with an increase in the values of tmax and (AUC)0 infinity, which are related to the serum creatinine concentrations, used as an index of the degree of renal function.