Abstract: The invention provides a transdermal, transmucosal pharmaceutical composition suitable for substantially extra-vascular application of at least one biologically active substance to biological membranes of a mammal, comprising a pharmaceutical or cosmetic composition comprising propylene carbonate at least one oil or source of fatty acid or surfactant; and water; in combination with the at least one biologically active substance wherein the propylene carbonate is adapted to enhance the bioavailability of the at least one biologically active substance.