The pharmacokinetics of 7-[D-(-)-alpha-amino-alpha-(4-hydroxyphenyl)-acetamido]-3-methyl-3-cefen-4-carboxylic acid (cefadroxil) were studied in rabbits with normal renal function and with varying degrees of experimentally caused renal impairment. All the animals included in the survey received a single i.v. dose of 30 mg/kg of the antibiotic. The following variations may be observed in the parameters established for the rabbits with altered renal function with respect to the rabbits with normal renal function: alpha, beta,K12, K21, K13, Vc and Vp decrease, and t 1/2 alpha, t 1/2 beta, and (AUC) infinity o increase. Linear relationships are established between the plasma urea and creatinine values, indices of the degree of renal function, and log k13. There is an increase in biliary excretion in rabbits with renal impairment and a linear relationship between the percentage of the antibiotic excreted and the plasma urea and a creatinine values. In rabbits with normal renal function a linear relationship may be found between the elimination rate of the drug in urine and the plasma concentration of the antibiotic.