The experiments with different triterpenoid saponins showed a significant difference in the microphysiometric activity between acylated and non-acylated compounds. Only acylated saponins in low concentrations were able to activate the metabolism of endothelial cells after short-time incubation in a transient manner lasting approximately 2 hours. The strongest effect was produced by virgaureasaponin b, an incubation with 4 microg/ml over 6 min induced a stimulation of the metabolic activity of 190% maximum after 30 min. This treatment did not induce non-reversible toxic effects, and could be repeated in the same way after a recovery period. The saponins without acylation in the glycosidic part did not induce metabolic stimulation, even in concentrations higher than observed for the acylated compounds. The current interpretation of the results is connected with the suggestion that especially acylated saponins are able to integrate into the cellular membrane transiently. This integration might induce pore-like structures which change the membrane permeability associated with alterations in the ionic homeostasis between intracellular and extracellular compartments.