A supported liquid membrane system was investigated for the carrier mediated transport of phenylalanine to more fully understand the contradictory effects, described in the literature, of chloride ion concentration in the aqueous phases on the stability of the system. The role of the organic phase and its interaction with carrier and support material was considered. The carrier mediated transport was comparable to an enzyme mediated process. Kinetic studies were undertaken and the data interpreted in a manner appropriate to biological transport processes to consider the transport process at a molecular level. The system was shown to deviate from a direct 1:1 exchange process between phenylalanine and chloride and had a high degree of selectivity with respect to phenylalanine.