A new hydrophobic and catalytic membrane was prepared by immobilizing beta-galactosidase on a polytetrafluoroethylene (PTFE) membrane, double grafted by means of gamma-radiation. Methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) were used as monomers to be grafted. 1-6 Hexamethylendiamine (HMDA) and glutaraldehyde (GA) were used as spacer and coupling agent,respectively. The membranes were characterized physically and biochemically. The values of the hydraulic and thermoosmotic permeability coefficients were calculated. The dependence of catalytic membrane activity on the temperature, pH and substrate concentration was studied. Lactose hydrolysis, performed under isothermal and non-isothermal conditions, confirmed the usefulness of employing non-isothermal bioreactors in industrial processes. In particular, characteristic parameters of the non-isothermal process, such as alpha and beta, indicative of the efficiency increase of the yield of an enzymatic reaction when a difference of temperature of 1 degrees C is applied across the membrane, were calculated. These values were compared with those obtained so far with other membrane systems.