A lipase-facilitated transport of 4-phenoxybutyric acid, 3-phenoxypropionic acid, 2-phenylpropionic acid, 2-phenoxybutyric acid, mandelic acid and 2-amino-2-phenylbutyric acid was carried out using a supported liquid membrane based on room temperature ionic liquids. There were marked differences in the permeate fluxes of various organic acids due to the substrate specificity of the lipases. The maximum permeate flux (44 x 10(-2) mmol cm-2 x h) was obtained using 4-phenoxybutyric acid as the substrate and 1-n-butyl-3-methylimidazolium hexafluorophosphate as the liquid membrane phase.