Cholesterol oxidase has been immobililzed on collagen films associated to an electrochemical sensor to form a “cholesterol electrode”. The electrode poised at a potential of + 650 my vs Ag/AgCl detects the hydrogen peroxide produced in the enzymatic reaction. This device presents a very high sensitivity and a wide range of linearity (10−7M - 0.8.10−4M). The use of a non enzymatic electrode associated with the enzymatic one allowed the detection and correction of electrochemical interferences when applied to human sera for free cholesterol determination.