The effect of monocrotofos (in a concentration of 4.5 X 10(-3)M) on the bioelectric parameters of rabbit intestinal epithelium was compared with a similar effect on these parameters of frog skin. It was demonstrated that the tested pesticide added to the medium on the mucosal side of the intestinal wall or on the external side of frog skin caused no evident changes in the potential difference (PD), short-circuit current (CC) and resistance of the studied tissues. This suggested absence of monocrotophos-binding receptors on the external surface of these epithelial structures. The pesticide applied to the serosal side of the intestine decreased PD and SCC without changing the resistance. Applied to the internal surface of frog skin it raised the PD and SCC with some decrease of the resistance. The different pattern of the response could be due to structural differences and to species-specific differences of these epithelia.