Prasugrel is a thienopyridine for treatment of acute coronary syndromes in patients undergoing percutaneous coronary intervention. Higher concentrations of prasugrel's active metabolite (R-138727) have been observed in Asian than white subjects. The primary objective was to investigate pharmacokinetics of R-138727 in healthy Korean males. Thirty subjects were randomized (1:2) to a 60 or 30 mg loading dose, subsequently (1:1:1) to 10-, 7.5-, or 5-mg maintenance doses. R-138727 plasma concentrations were analyzed with liquid chromatography/mass spectrometry. Platelet aggregation was measured with Accumetrics VerifyNow. Mean (coefficient of variation) exposure to R-138727 was 600 ng·h/mL (16%) after 60 mg prasugrel and 283 ng·h/mL (17%) after 30 mg. After 10, 7.5, and 5 mg, mean exposures were 78.1 (24%), 58.4 (21%), and 38.3 ng·h/mL (24%). Pharmacokinetics were linear over this range. Daily 5 mg doses maintained a 65% (SD = 14.5%) inhibition of adenosine diphosphate–induced platelet aggregation; all other doses produced ≥90%. Prasugrel was well tolerated with no serious adverse events. Results are consistent with other studies of Asian subjects administered prasugrel. Although further guidance will be provided by a recently completed phase 3 study, these preliminary data suggest that dosing strategies approved for white patients with acute coronary syndromes are applicable to Asian patients.