Defibrination with ancrod has been shown to be a successful form of treatment for certain types of experimental glomerulonephritis. The effect of ancrod on reticuloendothelial function has received little attention. In the present studies the blood clearance and reticuloendothelial uptake of injected preformed BSA-anti-BSA complexes were studied in defibrinated and control mice. 3 h after their injection, the blood levels and the hepatic and splenic uptakes were significantly different in experimental and control groups. It may be concluded that the reticuloendothelial clearance of injected immune complexes is not impaired by defibrination.