Poly(beta-acryloxypropionic acid) (PAOPA) hydrogels crosslinked by ethylene glycol dimethacrylate (EDMA) have been prepared by using both a chemical initiator and by gamma-irradiation. Polymerizations were conducted in bulk and also in the presence of water. Characterizations were made by swelling, compression-strain measurements and differential scanning calorimetry (d.s.c.). The findings show the following : (a) that gamma-irradiation is the preferred preparative procedure, (b) the equilibrium water content is affected by the concentration of crosslinker, but not by the content of water in the feed mixture, (c) the equilibrium water content increases with increase in the swelling temperature, and (d) there is considerable heterogeneity of crosslinking, as evidenced by calculated curves of instantaneous copolymer composition vs. fractional conversion during the crosslinking copolymerization. Similarities with and significant differences from the properties of poly(2-hydroxyethyl methacrylate) hydrogels are indicated and discussed.