Background & objectives: Agents that increase the permeability af intestinal epithelium promote the absorption of nutrients by the gut. High calcium concentration in the gut has been shown to enhance passive transport of glucose in the rat intestine. An increase in the permeability of the intestinal epithelium may account for this observation. The present study was aimed at monitoring the permeability of intestine of rats fed high or low calcium diets. Methods: Everted intestinal sacs were used to study transports of substances across the gut. While radioactive and non radioactive calcium isotopes were employed to study the active transport and passive transport of calcium, transport of labelled mannitol was taken as a measure of passive permeability.