A procedure for the determination of KR-30075 and its metabolites in plasma and urine by high performance liquid chromatography is described. For the study of pharmacokinetic properties of KR-30075, a new PDE III inhibitor, the plasma concentration and urinary excretion after an oral administration of KR-30075 (4 mg/kg) in the male rat (Sprague Dawley) were determined by high performance liquid chromatography. The best extraction efficiency of KR-30075 and KR-30072 is obtained with ethyl ether adjusted to pH 4.0. Retention times of both KR-30072 and KR-30075 were within 5 min and resolution was complete at the flow rate of 1.0 ml/min. The sensitivity and specificity of this HPLC assay appears to be satisfactory for the pharmacokinetic study of KR-30075 and its metabolites. One-compartment open model with first-order absorption was applied to evaluate the pharmacokinetic parameters of KR-30075 according to Minimum AIC Estimation. $T_{max}$ was 1 hr, $C_{max}$ was $0.789{pm}0.31;{mu}g/ml$ and elimination half $T_{1/2}$ was 6.31 min after oral administration of 4 mg/kg KR-30075 to male rats.