We studied splenic macrophage reticuloendothelial function in 18 patients with idiopathic membranous nephropathy and eight patients with mesangio-capillary glomerulonephritis by measuring the clearance from the circulation of technetium labelled, autologous, antibody coated erythrocytes (IgG cells) or heat damaged erythrocytes (HDE). Nine of 15 rhesus-D positive patients with membranous nephropathy had delayed clearance of the IgG cells and the defect did not correlate with disease activity. Circulating immune complexes were not detected in any of the patients with membranous nephropathy. The defect in clearance of the IgG cells in the membranous patients was associated with the presence of HLA-B8 and DR3. In the mesangio-capillary glomerulonephritis patients, the clearance rates of the IgG cells were fast-normal in six and enhanced in two, and correlated with the clearance of HDE. The clearance rates of the cells in this group correlated with the degree of hypocomplementaemia but not with the disease activity nor HLA haplotype.