Specially treated nylon 66 strips were exposed to sorbic acid solutions at a number of different concentrations and at several temperatures and the quantity of drug sorbed determined by suitable means. Thermodynamic and kinetic treatment of the data permitted the evaluation of a number of constants such as ( a ) saturation value of drug in the plastic, ( b ) affinity of drug toward the plastic, ( c ) standard heat of sorption, ( d ) apparent diffusion coefficient, and ( e ) activation energy of diffusion. Changes in concentration of solution influenced both the apparent diffusion coefficient and the activation energy of diffusion. A nearly linear relationship was noted between the concentration of the solution and the diffusion coefficient, the diffusion coefficient decreasing with an increase in concentration of solution. The standard heat of sorption suggested that the interaction between the sorbic acid and the nylon might be due to a double hydrogen bond formation.