A new possibility of using variations in the permeability of liquid membranes for sensing cholesterol in aqueous media has been explored. The method is based on the enhancement of conductance of the lecithin-prostaglandin and lecithin-nystatin liquid membrane bilayers due to the formation of hydrophilic pathways by the addition of cholesterol. Since enzyme is not used, the stability of the device is not governed by the stability of the enzyme. The response time of the device is less than 60 s. The device using prostaglandin has been tested by estimating free cholesterol in blood serum and it works well. (C) 2000 Elsevier Science B.V. All rights reserved.