The optimisation of the intestinal absorption of drugs represents one of the most important steps in the development of new pharmacologically active products. Several in vitro models are commonly used to study the mechanisms involved in drug absorption and all have advantages and disadvantages, notably they are often very static, and rarely take into account the intestinal motility and blood flow. The aim of this project was to validate a new ex vivo/in vitro model to study drug absorption, the perfused everted intestinal segment of rat, using three absorption markers: antipyrine (CAS 60-80-0) for passive transcellular diffusion, mannitol (CAS 69-65-8) for the paracellular diffusion and digoxin (CAS 20830-75-5) as a P-glycoprotein substrate. The mean apparent permeabilities (P(app)) for the markers were 6.07 (+/- 0.99) x 10(-5), 8.79 (+/- 0.28) x 10(-6) and 3.1 (+/- 0.85) x 10(-5) cm/s, respectively. The model is simple to establish and gives excellent absorption kinetics (r2 > 0.99), providing a valuable tool to study drug absorption during preclinical development, and subsequently the effects of different pharmaceutical formulations on that absorption.