Rats with classic Goldblatt (two-kidney) hypertension had diabetes induced by streptozotocin. After four months of diabetes, glomeruli of the unclipped kidney of hypertensive diabetic rats had markedly increased diabetic changes, including mesangial matrix thickening and mesangial immunoglobulin (IgG and IgM) and complement (C3) localization, when compared with glomeruli of the contralateral-clipped kidneys. Further, glomeruli of the unclipped kidneys of hypertensive diabetic animals had more mesangial thickening and IgG and IgM staining than glomeruli of normotensive diabetic rats. Although glomeruli of clipped kidneys in hypertensive diabetic rats had less mesangial thickening than glomeruli of normotensive diabetic rats, this did not reach statistical significance. However, these glomeruli did have significantly less IgG, IgM, and C3 staining compared with glomeruli of normotensive diabetic animals. Mesangial thickness in glomeruli of clipped and unclipped nondiabetic hypertensive rats did not differ from that in normal animals. However, there was less mesangial IgG staining in clipped than in unclipped kidneys of nondiabetic hypertensive rats or in kidneys of normal animals. We have interpreted these results to imply that alterations in nephron hemodynamics combine with the diabetic state to influence the rate of development of diabetic glomerulopathy in rats.