HLA antigen B12 is in linkage disequilibrium with HLA antigen Cw5. In some way this particular haplotype seems to be associated with a mechanism increasing serum transcortin levels. As shown before, the latter mechanism does not involve elevated estrogen levels or a generalized increase in glycoprotein synthesis. Similar high transcortin levels (more than 2 SDs above the mean) are found frequently in patients with lymphatic leukemia, hairy cell leukemia, or non-Hodgkin lymphoma, as well as in the siblings of these patients. HLA antigen Bw35 is in linkage disequilibrium with HLA antigen Cw4. Transcortin levels in patients with this combination of HLA antigens are significantly lower than in patients who do not carry these two antigens. Relatives of subjects with very low transcortin levels often have the same low levels. These findings together with recent data in the literature suggest that a cluster of genes regulating certain aspects of glucocorticoid metabolism is located in the vicinity of HLA locus B and C.