Enzymes are immobilized on activated carbon supports at high load levels and with high stability by a procedure whereby a carbon support is first activated with a water-soluble carbodiimide derivative which forms a highly reactive intermediate with carboxyl and other active organic radicals on the surface of the carbon support; thereafter the complex of the carbon and carbodiimide is treated with an enzyme solution whereby the enzyme displaces the carbodiimide and forms a carbon-enzyme complex wherein the enzyme is immobilized and yet the carbon retains its surface activity. Preferred immobilizing agents are quaternary ammonium forms of aminocarbodiimides or hydrochloric acid salts of water-soluble carbodiimides. The immobilization of the enzymes on activated carbon provides materials which are easily handled and which are stabilized against denaturation by hydrogen peroxide.