The use of tris(hydroxymethyl)phosphine as a coupling reagent for the immobilization of alcohol dehydrogenase onto chitosan films and for the attachment of the chitosan film to a glass support resulted in enzyme activities far above those obtained by adsorption of enzyme, and greater than those observed when using the more conventional glutaraldehyde-coupling protocol. The stability of the chitosan films was dramatically increased by covalent attachment to the glass using tris(hydroxymethyl)phosphine. Similar enzyme activities were found for coupling with tris(hydroxymethyl)phosphine and glutaraldehyde on aminopropyl silica and aminopropyl glass. The tris(hydroxymethyl)phosphine coupling extended the longevity of the alcohol dehydrogenase activity brit did not alter the pH optima or K-m of the enzyme.