MK-0767, a dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist, has been studied as a potential treatment of type 2 diabetes and dyslipidemia. The pharmacokinetics and interconversion of (+)-(R)-MK-0767 and (-)-(S)-MK-0767 were evaluated following oral administration of each single enantiomer and the racemate to healthy subjects. The results demonstrate that, consistent with in vitro experiments, chiral inversion occurs rapidly in vivo, and interconversion equilibrium favors (+)-(R). After all treatments, a stable ratio (R/S) of 2 to 2.5 was achieved within 8 hours in most individuals, congruent with model-based estimates of interconversion half-life. In addition, the pharmacokinetics of each enantiomer were generally similar regardless of treatment. Modeling and simulation of enantiomer disposition suggest that the observed predominance of (+)-(R)-MK-0767 in plasma may result from differential volumes of distribution between (-)-(S) and (+)-(R), preferential conversion from (-)-(S) to (+)-(R), or a combination of these, but not faster clearance of (-)-(S) compared to (+)-(R).