Liposomes were prepared from dipalmitoyUecithin, dimydstoyllecithin, dioleoyUecithin, egg lecithin, and soybean lecithin, and the effects of incorporation of various quantities of a-tocopherol or its analogs on permeability of the liposomes to glucose were studied at various temperatures (4-40°C). Results showed that increase in the quantity of a-tocopherol incorporated into dipalmitoyUecithin and dimyristoyilecithin liposomes lowered the transition temperature for marked release of glucose and also decreased the maximum rate of temperature-dependent permeability, a-Tocopherol also had similar but less marked effects on the permeability of dioleoylleeithin and egg lecithin liposomes, but little effect on those of soybean lecithin, which has a higher degree of unsaturation. In dipaimitoyUecithin liposomes phytol showed a similar effect on permeability to that of a-tocopherol, but phytanic acid caused a different pattern of temperature-dependent permeability. With analogs of a-toeopherol, the regulatory effect on permeability decreased with shortening and disappearance of the isoprenoid side chain. The significance of these observations is discussed in relation to the physiolo#eal functions of tocopherols in natural membranes.