Abstract
In this report, two case examples on species difference between human and experimental animals are introduced. They are related to drug absorption from the lower gastrointestinal tract, which were observed in studies of the oral controlled release formulation design. Both examples showed lower colonic absorption in human than that in experimental animals （dog and monkey）. Although it is difficult to determine the relationship in characteristics of the colonic absorption between human and experimental animals only based on the examples, the result will be expected to be informative to discuss the predictability of the bioavailability of oral controlled release formulations in human from the results of the bioavailability studies in experimental animals.
