The permeabilities of isoniazid and amitriptyline hydrochloride in chitosan membranes were investigated. Drug concentration was changed from 0.1 to 1.0% while membrane thickness was varied from 40 to 150 mum. The release rate was measured in water at 30 +/- 0.1degreesC by spectrophotometric determination. The drugs presented quite different permeabilities, which were related to their molecular weights; the permeabilities did not change with thickness or drug concentration for the ranges investigated.