One hundred and seventy-nine patients with various forms of glomerulonephritis confirmed histologically were tested for HLA A and B antigens: Thirty-four with membranous glomerulonephritis were also typed for DR antigens. One hundred and forty-one of these patients were further tested for blood group, red cell enzyme, and plasma protein systems. The minimal-change and the mesangio-capillary glomerulonephritis showed a significant association with B8 and Bw44 antigens respectively, whereas the membranous nephritis in addition to B8 was also found to be associated with DR3 antigen. Previously described associations with Henoch-Schönlein and Berger's nephritis were not proved. A large group with nonspecific proliferative glomerulonephritis did not show any association with HLA. Among the other single-gene characters studied, a significant association was found with Bf (Factor B or C3 proactivator) and adenosine deaminase, both markers thought to be involved in the immune response. The close association of the markers located on chromosome 6 and glomerulonephritis indicates that there may be an immunological component in the aetiology of the disease. The significance of the various associations found is discussed.