The use of mineral acid to enhance the radiation grafting of monomers to trunk polymers such as polyethylene is shown to be of value for the insolubilization of enzymes and the hetero-genization of catalytically active homogeneous complexes. Two general methods are described showing how acid enhancement effects can be used in the immobilization reactions. In the first technique, styrene is grafted, and the resulting co-polymer can be nitrated followed by subsequent chemical reactions to yield an appropriate substituent to which the attach ment processes can occur. Alternatively, p-nitrostyrene can be grafted directly. In the latter method, the acid enhancement is shown to be valuable, since the monomer is deactivating in radiation grafting and any technique for improving yields is useful. The acid enhancement effect is also shown to be of value for grafting to polyethylene, since this backbone polymer is less susceptible to grafting than the other two trunk polymers studied, i. e., polypropylene and PVC. A novel mechanism for the acid effect is proposed. The grafting of p-nitrostyrene is more satisfactory for the insolubilization reactions when compared with the alternative of styrene grafting followed by nitration.