A time-resolved fluorometric immunoassay for water-soluble H antigens of ABH blood group substances has been developed. Introducing artificial antigens (trisaccharide-albumin complexes for H type 1 and H type 2) as reference substances, H blood group substances in human saliva were measured. The monoclonal antibody, anti-H 1E3, reacted with both H type 1 and type 2 chains, and the commercially available anti-H reacted with H type 2 chain. Using these two antibodies we found 10-20-fold higher concentration of H type 1 compared with that of H type 2 in human saliva. The H type 2 was not found in the saliva samples from nonsecretors, irrespective of ABO phenotypes. The results suggest that approximately 90% of A and B blood group substances in human saliva are built on type 1 chains.