The sequential intravenous injections of protamine and heparin into rats results in the deposition of protamine-heparin aggregates along the lamina rara externa of the glomerular basement membrane. Morphologic studies indicate that these foreign aggregates are removed from the glomerular basement membrane by virtue of phagocytic activity by the glomerular visceral epithelial cells. We have studied the disappearance rate of protamine-heparin aggregates from the glomerular basement membrane in animals given a single dose of these compounds and in animals receiving chronic administration. The disappearance rate was measured utilizing a computerized morphometric technique to determine the numerical density of protamine-heparin aggregates per 100 µm glomerular basement membrane in sequential biopsy specimens taken from 15 to 600 min post-injection. The disappearance rate described a linear function in both acute and chronic animals, with a half-disappearance time of approximately 120 min. Disappearance of the aggregates appeared to be due to epithelial cell phagocytosis. This model provides a method of studying this function in the intact glomerulus in both normal and disease states.