Abstract: The subject invention describes a method of determining the secretor status of an individual which comprises obtaining a sample of a biological fluid from the individual and determining whether the sample includes the Lewis.sup.a or Lewis.sup.b antigens, the presence of the Lewis.sup.a antigen in the sample indicating that the individual is a nonsecretor, the presence of the Lewis.sup.b antigen in the sample indicating that the individual is a secretor, and the presence of neither antigen indicating the secretor status of the individual is inconclusive. The invention also provides a method of further determining the secretor status of an individual of having an inconclusive secretor status which comprises determining whether the biological fluid sample from the individual includes A, B or precursor type 1 chain antigens, the presence of any such antigens in the sample indicating that the individual is a secretor, the lack of any such antigens in the sample indicating that the individual is a nonsecretor.