The dynamic and equilibrium swelling behavior are reported for four γ-irradiation cross-linked elastic protein-based polymers comprised of repeating pentapeptide sequences. The elastomeric polypentapeptides, previously prepared using recombinant DNA technology, are (GVGVP)251, (GVGIP)260, (GVGVP GVGVP GEGVP GVGVP GVGVP GVGVP)35](GVGVP), and (GVGVP GVGFP GEGFP GVGVP GVGFP GFGFP)35](GVGVP), where G = glycine, V = valine, P = proline, I = isoleucine, F = phenyalanine, and E = glutamic acid. These polymers had been γ-irradiation cross-linked into elastic matrices using doses ranging from 6 to 34 Mrad. Fick's law was able to explain their initial dynamic swelling behavior. Thermal history was found to be a variable affecting dynamic swelling. The equilibrium swelling ratio was dependent on both temperature and pH (for the E-containing polymers) and analyzed using the Flory-Huggins interaction parameter. The interaction parameter could be related with the Tt mechanism developed for polypeptides. Different continuities found in the phase transitions of these polymers and poly(N-isopropylacrylamide) were discussed in terms of cooperative units.