A method is described where teeth are sectioned/ground along at least two planes, etched, and viewed at various angles in the SEM in order to study the three-dimensional structure of enamel. This multiplane sectioning-scanning electron microscopy (MPS-SEM) method has been applied to the study of rat and human enamel. The method demonstrates in a direct way the complex three-dimensional structure of rat incisor enamel; the path of prisms and the distribution of interprismatic substance. The different appearance of alternate prism rows as seen in the longitudinal plane is seen to be due to prisms in alternate rows being inclined to different degrees in the transverse plane. In human enamel, the method reveals the three-dimensional nature of Retzius lines. In tangential planes cut at right angles to the prisms, Retzius lines are identified on the basis of an altered size, shape or etching pattern of prisms. Considerable variation in etching pattern within the same tangential plane was observed. Enamel tufts could be observed simultaneously in tangential and longitudinal planes, giving information about their three-dimensional extent and their relationship to Hunter-Schreger bands and to prisms and interprismatic substance. The main advantage of the method is that deduction of three-dimensional structure from the appearance of the structure in one plane is aided by the appearance of the structure in the adjoining plane.