An enantioselective high-performance liquid chromatographic method for chloroquine and desethylchloroquine was developed using a chiral alpha 1-acid glycoprotein column. This method was used to determine concentrations of chloroquine and desethylchloroquine enantiomers in plasma and urine from volunteers given single oral doses of racemic chloroquine. The disposition of the enantiomers was different. The renal clearance of the chloroquine enantiomers was indicative of stereoselective renal secretion of the drug, and evidence for stereoselective metabolism also was found.