In most of our patients with idiopathic membranous nephritis (MGN), we have studied the HLA-A, B, DR phenotype, the clearance of anti Rhesus D coated-51 Cr-labeled-autologous erythrocytes, and the peripheral blood T-lymphocyte subpopulations as ascertained by monoclonal antibodies (OKT3, OKT4, OKT8). The frequency of HLA-B8 antigen is 57.14% in 28 primary MGN versus 14.4% in 104 local controls (Pc less than 0.00018). The frequency of HLA-DR3 antigen is 65.38% in 26 primary MGN patients versus 20.27% in 74 local control individuals (Pc less than 0.00008). The half-life of sensitized erythrocytes is 37.30 +/- 9.55 min in 10 controls, 1963 min and 1601 min in 2 splenectomized controls, 12 min in a patient with hypersplenism, and 67.05 +/- 69.64 min in 18 idiopathic MGN patients respectively. The half-life is significantly prolonged in 6 out of 18 MGN patients. This prolongation correlates with exacerbation of the disease while normal values are obtained with remission. The OKT3 positive subpopulation (total T-lymphocytes) is 63.77 +/- 10.37% in 31 controls versus 53.74 +/- 13.81% in 22 MGN (P less than 0.002). The OKT4 positive subpopulation (helper T-cells) is 37.90 +/- 8.21% in controls versus 32.79 +/- 10.89% in MGN (P less than 0.03). The OKT8 positive subpopulation (suppressor T-cells) is 21.60 +/- 5.28% versus 20.03 +/- 5.76% respectively. The OKT4/OKT8 ratio is 1.85 +/- 0.58 in controls versus 1.74 +/- 0.69 in MGN. During exacerbation, the T-lymphocyte subset fractions are normal, whereas OKT3 and OKT4 are decreased during remission. MGN is a strongly HLA-linked disease.(ABSTRACT TRUNCATED AT 250 WORDS)