The enantiomeric composition of carprofen has been determined in a rapid and reliable manner by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide-shift chelate. Carprofen was converted into a mixture of enantiomeric methyl ester derivatives which were then complexed with tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium(III) in CDCl(3). The concentration of substrate in the test sample was 0.15M and the chiral-shift reagent:substrate molar ratio was 0.453. Determination of the enantiomers was based on the relative intensities of the signals for the alpha-methyl protons. The mean recovery +/-SD for six determinations of S(+)-carprofen from synthetic enantiomeric mixtures was 99.3 +/- 1.7%.