D: -Amino acids are now recognized to be widely present in mammals. In rats, exogenously administered D: -methionine is almost converted into the L: -enantiomer via 2-oxo-4-methylthiobutylic acid as an intermediate. D: -Amino acid oxidase is associated with conversion of D: -methionine into the 2-oxo acid. Since D: -amino acid oxidase is present at the highest activity in the kidney compared to other organ, kidney injury is suggested to cause accumulation of D: -methionine. The purpose of the present study is to assess the role of kidney in the elimination of D: -methionine and metabolic conversion into L: -methionine in rats using a stable isotope methodology. After a bolus i.v. administration of D: -[²H₃)]methionine to 5/6-nephrectomized rats, plasma concentrations of D: -[²H₃]methionine, L: -[²H₃]methionine, and endogenous L: -methionine were determined by a stereoselective GC-MS method. Renal mass reduction slowed down the elimination of D: -[²H₃]methionine. The clearance values of conversion of D: -[²H₃]methionine into the L: -enantiomer in 5/6-nephrectomized rats were one-sixth of those in sham-operated rats. The elimination behavior of D: -[²H₃]methionine observed in rats demonstrated that kidney was the principal organ responsible for chiral inversion of D: -methionine.