Five issues are addressed. One issue is the structure of H-, A-, and B-active saccharides isolated from the globoside fractions from human erythrocytes. A second issue reviewed is the enzyme characterization of a blood group A-gene specified alpha-N-acetyl-galactosaminyltransferase (A-enzyme), and a blood group B-gene specified alpha galactosyltransferase (B-enzyme). Other issues considered are the immunological properties of the A-enzyme and B-enzyme, the cDNA structures of human blood group ABO genes, and transcriptional regulation of the human blood group ABO genes. Regarding the latter issue, the authors clarified the regulation of the ABO gene expression by investigating a human genomic DNA clone, HG-1, which contained exon 1 and 4.7 kbp of the 5'-flanking sequence of the ABO genes. The studies suggest that DNA methylation of the ABO gene promoter may play an important role in cell type-specific expression, as well as an altered expression during tumorigenesis. The experimental result showed that there were two loci of polymorphism: VNTR of a 43 bp consensus sequence (ABOU1) and an insertion/deletion polymorphism of the 35 bp DNA segment (ABOU2). 2 figures and 42 references