Mass transfer data are obtained for the adsorption of phenylalanine in porous polymeric adsorbents with different pore structures and Functionalities. In most cases, the data are adequately described by assuming that hindered diffusion in liquid-filled pores is the controlling mass transfer mechanism. For these adsorbents, the ratio of particle porosity and tortuosity factor is found to be essentially constant as a function of temperature and composition of the liquid phase. The tortuosity factors are somewhat larger for the smaller pore materials than for the larger-pore ones. However, in the case of a nearly microporous adsorbent, the diffusivity appears to be dependent on temperature to an extent which is not consistent with the assumption of diffusion in rigid, liquid-filled pores.