The release from matrixes compressed from melts of hydrogenated castor oil and ephedrine hydrochloride or procaine hydrochloride has been studied and is compared with the release from matrixes prepared by compression of physical mixtures. In both, the release is dependent on the square root of time; however, the release is slower from the matrix prepared by the melt process. Parameters that affect the release are compared. The independence of release from stirring speed and the greater tortuosity of the matrix prepared by the melt process indicate that the release is by a matrix diffusion mechanism. In contrast, boundary layer diffusion is operative in the release from the matrixes prepared by compression of physical mixtures. It is demonstrated that for a given formulation, the method of processing may alter the mechanism and rate of release.