A carrier mixture of lipophilic boronic acid and bis(quaternary ammonium cation) greatly facilitates the transport of ribonucleoside monophosphates through liquid organic membranes, at neutral pH. Transport selectivity was determined for the isomers of GMP. The observed order of noncompetitive transport rates war 5'-GMP > 2'-GMP > 3'-GMP. Copyright (C) 1996 Elsevier Science Ltd