The coincidence of the presence of ABH active substances in the saliva of persons with those individuals who possess either LEWIS-d or LEWIS-b antigens on epithelial cells of their stomach tissues is examined in terms of the three-dimensional conformations of the oligosaccharide structures which form the ABH and LEWIS antigenic determinants. The H activity in saliva is normally established by examining the inhibition of the agglutination of human H red cells, which possess H (Type 2) determints at their surface, by the lectin Ulex europaeus. As was to be expected, the LEWIS-d (H-Type 1) (alpha LFuc (1 leads to 2) beta DGal (1 leads to 3) beta DGlcNAcOR, R = (CH2)8COOCH3) and LEWIS-b (alpha LFuc (1 leads to 2) beta DGal (1 leads to 3) [alpha LFuc (1 leads to 4)] beta DGlcNAcOR) determinants, obtained by chemical synthesis, do not bind Ulex. However, these structures in the de-N-acetylated form proved to do so as evidenced by their ability to inhibit the agglutination. These results together with results obtained in inhibition studies involving chemically modified H (Type 1) and H (Type 2) structures are rationalized in terms of conformational analysis and raise the possibility that the LEWIS-b and d antigens in saliva are present with the determinants in the amine form. The circumstantial evidence obtained in support of this possibility is, as yet, inconclusive. The main thrust of the paper is to indicate how modern conformational analysis may play an important role in the improvement of knowledge in carbohydrate-receptor site interaction.