The pharmacokinetic behaviour of cefadroxil was dose-dependent in healthy male volunteers following the oral administration of single doses of 5, 15, and 30 mg.kg-1. As the dose of cefadroxil increased from 5 to 15 and 30 mg.kg-1, the peak plasma concentrations, normalized to 5 mg.kg-1, decreased significantly from 15.1 to 10.7 and 7.6 mg.l-1, while the corresponding normalized areas under the plasma concentration-time curves from 0 to 2 h decreased significantly from 1258 to 946 and 801 min.mg.l-1. When the same subjects were given 5 mg.kg-1 of cefadroxil together with 45 mg.kg-1 of cephalexin, the absorption of cefadroxil was slowed to a similar or greater extent than with the high dose of cefadroxil. Although the absorption rate decreased as the dose increased, the systemic availability of cefadroxil was essentially complete at all doses, as judged by the 24 h urinary recoveries of the antibiotic. Kinetic analysis of the plasma concentration-time curves gave the best fit with a zero-order followed by a first-order absorption process, consistent with saturable intestinal absorption of cefadroxil. The elimination rate of cefadroxil was directly related to dose and plasma concentrations, and the clearance at the dose of 5 mg.kg-1 was significantly increased by the simultaneous administration of high-dose cephalexin. The renal clearance of cefadroxil ranged from 98 ml.min.l-1 at total plasma cephalosporin (cefadroxil + cephalexin) concentrations less than 2.5 mg.l-1 to 156 mg.l-1 at concentrations greater than 40 mg.l-1.(ABSTRACT TRUNCATED AT 250 WORDS)