Although sheep erythrocytes do not activate the alternative complement pathway (ACP) of human serum, the erythrocytes gain a capacity to activate human ACP following removal of membrane sialic acid by neuraminidase treatment1–3. Therefore, asialoglycoconjugates generated from sialosylglycoconjugates by neuraminidase treatment might be responsible for this type of ACP activation on cell membrane4. Alternatively certain sialosylglycoconjugates on the cell membrane might restrict the activation of ACP and removal of the terminal sialic acid from the glycoconjugates would abolish this restricting capacity and result in activation of the ACP on the cell membrane5. To determine which of the above two possible mechanisms is the case, we used a liposome model membrane in which glycolipids could be artificially inserted, and our results suggest that the latter of the two possible mechanisms is the case.