Abstract: An isolated nucleotide sequence encoding human leukotriene C4 synthase or variants of human leukotriene C4 synthase polypeptide, is provided. One embodiment is an isolated DNA sequence (SEQ ID NO.:1) encoding a human leukotriene C4 synthase polypeptide, that has three hydrophobic transmembrane domains. Also described are recombinant cells and plasmids containing the foregoing isolated DNA, preferably linked to a promoter. Isolated leukotriene C4 synthase is provided, having at least three hydrophobic transmembrane domains (SEQ ID NO.:2). Portions of the foregoing isolated human leukotriene C4 synthase polypeptide are also described. Antibodies with selective binding specificity for the polypeptides of the invention also are provided as well as a sensitive method for assay of human leukotriene C4. Methods for producing leukotriene C4 synthase as well as methods for testing for modulators of leukotriene C4 synthase activity are also described.