The influence of some amino acids-alanine, glycine, valine, glutamine, histidine, phenylalanine, and tryptophan-on the swelling behavior of acrylamide (AAm) hydrogel prepared by gamma-radiation was investigated. Swelling experiments of AAm hydrogel were made in the universal buffer solutions and the amino acid solutions at certain pHs at 37 degrees C. These selected pH values were pK(1), pK(2) and isoelectric point (pI) values such as ionization of alpha-carboxyl groups, ionization of alpha-amino groups, and the pls of the amino acids, respectively. The swelling of AAm hydrogel increased when pH values of solutions were increased. The value of equilibrium swelling of AAm hydrogel in the solution of universal buffer was 880% at pH 10.0, whereas it was 670% at pH 2.0. The values of equilibrium swelling of AAm hydrogel in amino acid solutions were between 830 and 965% at pH 10.0, whereas they were between 635 and 775% at pH 2.0. The rate constant of swelling, initial swelling rate, theoretical maximum swelling, diffusional exponent, network parameter, and diffusion coefficient were calculated by swelling kinetics. Diffusions of the amino acid solutions into the hydrogel were generally found as non-Fickian in character. The diffusion coefficients of the hydrogel were between 0.91 x 10(-6) and 2.41 x 10(-6) cm(2)/s.