The objective of this study is to determine the ultrastructure of amelogenesis in several mammals using the scanning and transmission electron microscopes in order to enhance our understanding of enamel formation and enamel structure. In this study we will separate the ameloblasts from the nascent enamel and scan both surfaces of the ameloblast-enamel interface to reveal a detailed relationship between the cells and the enamel they are secreting. The comparative aspect of this study is to examine amelogenesis in the rat, cat, dog and monkey in order to establish similarities and differences in enamel structure among these animals in order to evaluate their usefulness as experimental models comparable to human enamel structure. Emphasis will be given to uncovering basic principals of amelogenesis which are pertinent to all enamel systems. Emphasis will be given to cellular control by ameloblasts in crystallite orientation in both rod and interrod enamel, and on a larger scale, ameloblast movement resulting in various patterns of enamel rod decursation. Evidence will be sought pertaining to the function of the papillary layer and its relationship to reduced ameloblasts.