Transport mechanisms have been studied for amino acids such as p-amino benzoic acid and phenylalanine moving through a bulk organic liquid membrane system containing carboxylated poly (styrene) carrier. The transport in this system, in which one side of the membrane was acidic and the other side was alkaline, was influenced significantly by the initial H+ ion concentration on the acidic side. The passage of amino acids through the organic bulk liquid membrane was governed by an electrochemical interaction between carboxyl groups in the membrane and transporting materials. © 1995.