A N,N-dimethylacrylamide-based hydrogel (2) with the new cross-linker (ethylenedioxy) bis[2,2'-(N-acryloylamino)ethane] (1) has been prepared, and its physicochemical properties in aqueous solution were studied. Three different native proteins (lysozyme, bovine serum albumin, and rabbit IgG) were encapsulated within the polymeric matrix 2, and the kinetics of their release from the swollen hydrogel were determined. The rate of protein release exhibits a clear dependence on both the molecular weight of the protein and the amount of cross-linker utilized to prepare the hydrogel. This is reflected by the fact that the low molecular weight proteins are released at an increased rate versus higher molecular weight proteins. In addition a greater amount of protein is released from the hydrogels with a lower percentage of cross-linker. The polymerization procedure used in this study is sufficiently mild to safeguard the functional integrity of attendant biomolecules as determined by the retention of catalytic activity of encapsulated a-chymotrypsin and aldolase catalytic antibody 38C2. The potential utility of these hydrogels for the controlled release of bioactive agents in vivo is strengthened by both their lack of toxicity against human dermal fibroblasts and their lack of immunogenicity in mice.