Experimental partition coefficients were measured for the distribution of selected proteins and small biomolecules between aqueous, buffered solutions and hydrogels. Temperature-sensitive hydrogels were prepared by polymerizing N-isopropylacrylamide (NIPA) alone and by copolymerizing NIPA and a charged monomer. Temperature- and pH-sensitive hydrogels were prepared by copolymerizing NIPA with weakly acidic and/or weakly basic monomers. The effects of temperature, pH and ionic strength on partitioning were investigated. In general, protein partition coefficients ranged from 0 to 10 in buffers on 0.1 M ionic strength. pH had a significant effect on the partition coefficient for a protein into a weakly ionizable polyelectrolyte gel even at this ionic strength.