Disodium etidronate affected salicylic acid absorption from the rat small intestine, in-situ, when instilled into a jejunal segment for different exposure times before the salicylic acid absorption was measured. At low etidronate concentrations and short exposure times, the salicylic acid absorption rate was significantly increased compared with saline controls. At high etidronate concentrations and longer exposure times, the absorption rate was reduced. Etidronate precomplexed with calcium or magnesium ions at low concentrations still enhanced salicylic acid absorption but at high concentrations absorption of salicylic acid was close to saline controls. Intestinal mucosa exposed to high etidronate concentrations showed a progressive structural destruction but with the complexes, there was no visible alteration. It is proposed that a solubilized etidronate complex, formed either in-situ or administered as such, is responsible for enhancing salicylic acid absorption. This effect is hidden at high etidronate concentrations because of the deterioration of the mucosal surface and at high complex concentrations because these decrease the absorbing surface area and increase the viscosity of the lumen contents.