Several therapeutically active ingredients including benzocaine, cyclomethycaine, and methapyrilene hydrochloride were incorporated into ethylcellulose and polyamide films. The effect of cetyl alcohol and tributyl citrate upon the release of these ingredients was studied. The films containing the active ingredient and plasticizer were cast upon a mercury substrate, and the in vitro release of these drugs from each film into a desorbing medium of distilled water was measured. The results indicated that the film-forming agent and plasticizer affected the drug release rate and that the release followed first-order kinetics. Benzocaine was slowly released from polyamide-cetyl alcohol films and polyamide-cetyl alcohol-tributyl citrate films. Polyamide-tributyl citrate films showed enhanced release of benzoacaine and cyclomethycaine. Ethylcellulose films plasticized with tributyl citrate produced a fast drug release. Based upon these results, a water-soluble, highly polar, noncomplexing additive would tend to increase the drug release from the film. When the amount of benzocaine released from ethylcellulose was plotted as a function of the square root of time, a linear plot was obtained. Since this linear plot passed through the origin, ethylcellulose should be an ideal matrix for benzocaine according to the Higuchi diffusion-controlled model. These studies demonstrated the in vitro release of thf the solubility of the active agent in both the polymer film as a function of the solubility of the active agent in both the polymer matrix and the desorbing medium.