In this study, the absorption enhancing ability of a group of a unique series of fatty acid derivatives, ethyl glucoside esters, was evaluated. Esters of saturated C10-C18 fatty acids as well as an ester derivative of the unsaturated oleic acid were included in the study. Caco-2 monolayers were used as a model for the human intestinal epithelium. The effect of the ethyl glucoside esters on the intracellular dehydrogenase activity was determined using a staining method based on thiazolyl blue reduction, and cytoplasmic staining with trypan blue was used to characterize the degree of membrane perturbation caused by ethyl glucoside esters. It was found that ethyl glucoside esters of C10 and C12 fatty acids as well as the ester of oleic acid enhanced the penetration of a hydrophilic pore marker (PEG 4000) across the Caco-2 monolayers. The apparent permeability coefficient increased even at concentrations of ethyl glucoside esters which only showed minor toxic effects on the Caco-2 monolayers.