A fatty acid-binding protein was purified from male rat kidney by the method of Fujii et al. [(1987) Arch. Biochem. Biophys. 254, 552-558]. Based on the close similarity of amino acid composition and the identity of the amino acid sequence in the amino-terminal region, the fatty acid-binding protein was identified as ct2wglobulin, which is the major male-specific protein in rat urine. The amino-terminal residue of the isolated kidney protein corresponds to residue 10 of ct2u-globulin, suggesting that the protein has been proteolytically processed in the kidney. This fatty acid-binding protein could not be immunologically detected in female rat kidney.Fatty acid-binding protein; Globulin, ct2u-; Male-specific protein; (Rat, Kidney)