In a previous study (Regoeczi, E. &Hatton, M. W. C. (1976) Can. J. Physiol. Pharmacol. 54, 27–34) it was shown that the chicken (Gallus domesticus) does not possess a hepatic asialoglycoprotein receptor. In the present study the same conclusion is drawn for the duck (Anas platyrhynchos). For this reason these avian species were used to assess those changes in the distribution and catabolism of human asialotransferrin which take place in the absence of the asialoglycoprotein receptor of the liver.Data obtained from both birds indicate that desialylation does not significantly affect the capillary transfer rate and the extravascular pool size of transferrin but it does shorten the biological life time of the protein. The increases in fractional catabolic rate resulting from desialylation averaged at 18.2% in six chickens and 19.8% in five ducks, these values being close to those reported earlier for bovine, canine, porcine, rabbit and rhesus asialotransferrins in a mammalian system, namely the rabbit.It is concluded that the selective removal of sialic acid residues makes transferrin recognizable as being biologically different from the native protein. As the result of this recognition, asialotransferrin is cleared from the circulation at rates which are slightly but significantly higher than those for the unmodified protein.