The effects of potato and tomato glycoalkaloids and a saponin mixture from Gypsophila were investigated in cytotoxicity studies (neutral red uptake, mitochondrial MTT reduction and release of lactate dehydrogenase), using cultured cell lines of rat and human intestinal mucosal epithelium. Experiments to assess the effects of these compounds on the integrity of the intestinal epithelium were also carried out using preparations of isolated rat jejunum in vitro. By investigating the effect of these compounds on cultured cells and on intestinal tissue preparations, changes in membrane integrity, as evidenced by lactate dehydrogenase leakage in cell culture, could be confirmed in a system more relevant to the whole gut. Of the compounds tested, α-tomatine was consistently the most potent in all tests, and indications of a synergistic effect on membrane depolarization were observed between α-chaconine and α-solanine at total glycoalkaloid concentrations of less than 1 mM (< 0.86 mg/ml), with an optimum when the former comprised 25% of the mixture. An increase in the apparent permeability of the brush border was observed at sublethal concentrations of the compounds, and this may have important implications with respect to enhanced uptake of macromolecules, such as allergens, whose passage through the epithelium is normally somewhat restricted.