Intraperitoneal injection of anionic carbamylated bovine albumin derivatives induced glomerular epithelial cell foot process loss and increased urinary protein excretion, the severity of which rose with the dose administered. The effects induced at a given albumin dose were significantly lower than those previously measured after the administration of normal bovine albumin. The amount of epithelial cell foot process loss induced after the injection of carbamylated bovine albumin derivatives correlated well with the level of induced proteinuria but, at a given level of proteinuria, the amount of foot process was lower in these rats compared with those given normal bovine albumin. The results obtained are consistent with the interpretation that the more anionic carbamylated bovine albumin derivatives were not only filtered less readily at the glomerulus than their less negatively charged counterparts but were also reabsorbed to a lesser extent by the tubular epithelium.