The role of the surface activity of vitamin A has been studied in the light of the liquid membrane hypothesis of drug action. Transport of relevant amino acids such as serine, threonine, arginine, and histidine and various ions such as calcium, sodium, and potassium in the presence of liquid membranes generated by vitamin A has been studied. The data on the modifications in the permeability of relevant amino acids and ions indicate that the liquid membranes generated by vitamin A may also play a significant role in its physiological action. (C) 2004 Elsevier Inc. All rights reserved.