A series of transdermal permeation enhancers based on dicarboxylic acid esters was studied. Single-chain amphiphiles were markedly more effective than the double-chain ones. Monododecyl maleate, that is a cis derivative, was a more potent enhancer than its trans isomer, while the activity of succinates strongly depended on the donor vehicle. No difference between diastereoisomeric tartaric and meso-tartaric acid derivatives was found.