Antiendothelial cell antibodies and increased von Willebrand factor (vWF) levels are observed in many renal diseases. We studied renal morphology after administration of rabbit anti-human factor VIII-von Willebrand factor (FVIII-vWFc) gamma-globulin (IgG) in rats. Isolated perfusion of normal rat kidney with the antibodies disclosed rabbit IgG along glomerular endothelium and in mesangial areas. Systemic administration resulted in an identical antibody distribution. C3 deposits and few electron dense deposits were transiently noted. After 1 week the mesangial deposition of rabbit IgG had increased significantly, most likely reflecting increased release of vWF by the endothelium. Thereafter, the deposits gradually relocated into mesangial stalk and into the glomerular vascular pole, and they had vanished after 6 weeks. Except for a mild influx of leukocytes, no renal injury occurred. In conclusion, although FVIII-vWFc antibodies cause mesangial immune deposits, antibodies against other endothelial antigens are apparently needed to inflict renal damage.