Effect of taurine on drug absorption from the rat gastrointestinal tract was investigated by using in situ loop method for the stomach and in situ recirculation method for the small or large intestine. Aspirin absorption from the stomach or the small intestine was enhanced by the presence of taurine, but not from the large intestine. The absorption enhancement effect of taurine was not only site-specific, but also substrate-specific. Taurine increased the absorption of aminopyrine from the small intestine, but not from the stomach. On the other hand, the absorption of salicylamide, o-methoxybenzoic acid and o-ethoxybenzoic acid was enhanced in the stomach, although they were not influenced in the small intestine. Furthermore, among the taurine analogues investigated only homotaurine showed the taurine-like action in the small intestine. Glycine also increased the gastric absorption of aspirin. These effects were observed neither by the pretreatment of the intestine with taurine, nor by i.v. administered taurine. Taurine at the site of drug absorption, even at a low concentration, seems to influence the drug absorption due to its effect on the permeability characteristics of the mucosal membrane.