Abstract: This invention relates to a method for administering systemically active agents including therapeutic agents through the skin or mucosal membranes of humans and animals in a transdermal device or formulation comprising topically administering with said systemic agent an effective amount of a membrane penetration enhancer having the structural formula ##STR1## wherein X and Y, each, may represent sulfur, oxygen or two hydrogen atoms, A is a branched or a straight chain, divalent aliphatic radical having from 0 to 2 double bonds; R' is selected from the group consisting of H, a lower alkyl group having 1-4 carbon atoms, phenyl, lower alkyl or halogen substituted phenyl, acetamido, halogen, piperidinyl, lower alkyl or halogen substituted piperidinyl, carbalkoxy, carboxamide, and alkylformyl; m is 3-7; q is 2m-2x, wherein x equals the number of double bonds in the lactam ring and may be 1, 2 or 3, and R is CH.sub.3, ##STR2## wherein R" is H or halogen.