The oral route is still the most preferred and convenient route of drug administration for the majority of patients.  Problems with availability of human tissue resulted in in vitro permeability studies often being performed on specimens obtained from laboratory animals, which are then extrapolated to the human situation. In this study thawed porcine intestinal mucosa (frozen in liquid nitrogen and stored at –85^oC) was used as an in vitro permeability model for human intestinal mucosa using tritium-labelled permeants (17β-estradiol, r-arecoline, vasopressin, oxytocin and water). A flow-through diffusion apparatus (24 h, 20^oC, 1.5 ml/h) was used for the study. The mean and estimated mean steady state flux values for water, 17β-estradiol, r-arecoline, vasopressin and oxytocin were approximately 19%, 126% and 20%, 21% and 15% higher, through porcine intestinal mucosa when compared to human intestinal mucosa, respectively (P<0.05, F-test). Generally, porcine intestinal mucosa seems to be a good in vitro permeability model for human intestinal mucosa, although flux values were generally higher for the animal model. Large differences were observed between the human and animal tissues for some permeants. Differences between the permeability characteristics of the two types of mucosa must therefore always be considered when using porcine tissue as an in vitro permeability model for human intestinal mucosa.