Abstract: The sorption and rate of permeation of propranolol hydrochloride were measured asa function of drug concentration in the solution bathing rat skin in vitro. The sorption isotherm wasnonlinear, and can be expressed in Langmuir form. The lag time and apparent permeability coefficientthrough intact skin decreased as the concentration of donor compartment increased, and those throughstripped skin were not varied. These results indicate that an adsorption process existed when propra-nolol hydrochloride penetrated through the stratum corneum. Based on the adsorption- diffusiontheory, a mathematical formula was developed for expressing the relationship between the concentra-tion of drug and permeability coefficient through the skin quantitatively.