Encapsulation of antibodies isolated from chicken egg yolk (IgY) in egg lecithin/cholesterol liposomes was attempted. IgY was successfully encapsulated into the liposomes by using the dehydration-rehydration method. Electron microscopic observation demonstrated that the liposomes prepared by this method were large multilamellar vesicles with a diameter of several microns. The encapsulation efficiency was improved by increasing the rehydration temperature to 60 degrees C. The cholesterol/lecithin ratio also affected the efficiency, giving the highest value at a ratio of 1/4 (mol/mol). Some efflux of glucose through the liposomal membranes was observed, particularly for the liposome with a low cholesterol content, but that of IgY was not detected, irrespective of the cholesterol content. Encapsulation reduced the activity loss of the IgY antibodies under acidic conditions. IgY encapsulated in the liposomes was also markedly resistant to pepsin hydrolysis, which usually results in complete loss of activity with unencapsulated IgY, suggesting that liposomal encapsulation is an effective means for protecting IgY under gastric conditions.