Abstract Three experiments were performed to determine the α-crystallin binding capacity of bovine lens lipid vesicles. In one experiment lipid was kept constant (2.5 mg ml -1) and the α-crystallin concentration was changed (0.5 to 3.0 mg ml -1). In another experiment, α-crystallin was kept constant (1 mg ml -1) and the concentration of lipid was varied (0.25 to 3 mg ml -1). We calculated the binding capacity of the lipid to be 0.33±0.05 ( s.d.) mg α-crystallin (mg lens lipid) -1. This was confirmed by changes in the anisotropy and fluorescent intensity of a probe that partitions at the headgroup region of the lipid bilayer. Near 0.33 mg α-crystallin (mg lens lipid) -1the fluorescence intensity and anisotropy of the probe increases and plateaus which indicates that concomitant with α-crystallin binding, water is excluded from the head group region of the bilayer and the headgroup region becomes less mobile. It is possible that α-crystallin binding could protect and stabilize the lipid bilayer and decrease membrane permeability.