The pharmacokinetics of FK027, a new oral cephalosporin, were investigated in rats and dogs and compared with those of cefaclor, cephalexin and amoxicillin. Upon oral administration to either rats or dogs, FK027 produced higher and more sustained serum levels than the reference drugs, hence a longer half-life. After both oral and intravenous administration, the half-life of FK027 in dogs was approximately three fold that in rats. Although the concentrations of FK027 in rat kidney, liver and spleen were lower than those of cephalexin and amoxicillin, they were sustained similarly to the serum levels. The 24-hour urinary and biliary recovery rates of FK027 in rats after oral dosing with 100 mg/kg were 34.1 and 21.9%, respectively. The urinary excretion of FK027 was significantly lower than that of the reference drugs, however, the biliary excretion was higher. In dogs, 23.4 and 0.2% of the given dose of 40 mg/kg of FK027 was excreted in the 24-hour urine and bile, respectively. Bioavailability of FK027 after oral dosing was 38% in rats and 47% in dogs, as calculated from intravenous data. Binding of FK027 to serum protein in all species was the highest of the test drugs: 63% for human, 93% for dog, 61% for rat serum.