Organophosphorus hydrolase (OPH) has been incorporated within polyurethane foams during polymer synthesis as a means of reducing the enzyme's environmental sensitivity to alterations in pH and bleach-induced enzyme denaturation. Unfavorable losses of enzyme activity upon altered pH are reduced by covalently incorporating OPH within polyurethane matrices. Also, the stability of the immobilized enzyme under alkaline conditions is significantly enhanced. The bleach compatibility of OPH is also increased upon enzyme polymerization. Although a fraction of the increased bleach compatibility results from polyurethane oxidation, the covalent linkages between OPH and polyurethane directly enhance enzyme stability in buffered solutions of calcium hypochlorite bleach.