One of the purposes of mastication is to break down the food and enlarge the area of food particles. A method is described by which the masticatory efficiency is estimated by calculating the area of a chewed test material, gelatin-hardened by formalin. When test pieces, after being chewed, are placed in a water-soluble dye, the dye will diffuse into the particles, and consequently the dye concentration in the surrounding solution will decrease. The concentration of the dye solution is read from a photometer. A close correlation was found between the gelatin particle area and the reduction of the dye solution concentration. The method will be applied in clinical studies.