The behaviour of desialylated human and chicken acid α1-glycoproteins is reported in chickens. Although desialylation resulted in accelerated disappearance rates from the plasma of both proteins, nevertheless the asialoproteins were eliminated much more slowly than expected on the basis of earlier observations in mammals. Analysis of tissue radioactivities, including kidney, liver, lung and spleen, failed to demonstrate any accumulation of the labeled asialoproteins in the liver, which is contrary to the situation in mammals. The main pathway for the elimination of desialylated human acid α1-glycoprotein in the chicken is via the kidney (tubular catabolism and/or urinary excretion). The clearance of desialylated chicken acid α1-glycoprotein is more complex as it involves the kidney as well as the reticuloendothelial system.These findings indicate that, unlike mammals, chickens do not possess a hepatic plasma membrane receptor for asialoglycoproteins. This raises the possibility that the presence or absence of this specific receptor may constitute a fundamental biological difference between mammals and birds.