The teeth buds which are observed in some teratomas ought to provide a useful system for the study of the development of organ structures in these tumours. They exhibit well defined characteristics in space and time. In contrast with normal development tooth bud formation in teratomas display malformations and other observable characteristics which are primarily the consequence of defects in coordination of activities among cells. Cyto-differentiation appears to be normal and the defective organogenesis must represent a breakdown of the principles which underlie the organization of structures. The possible role of the environment in organizing structure is discussed. Teratomas are unique biological systems which display in a dynamic way a panoply of teratological developmental processes of which teeth buds represent a fragmentary, repetitive and conspicuous expression.