Is it possible that fully differential cells, cells that have acquired specialized functions and perhaps have lost some general properties, can change their nature, becoming cells of another type? Professor Okada has studied this problem extensively and introduced the term "transdifferentiation" to describe the phenomenon. Transdifferentiation is extremely controversial, since it challenges a number of biological orthodoxies. If transdifferentiation really does occur, the process of development and differentiation must be much more flexible than biologists have generally believed. In this book, the author brings together a vast amount of experimental evidence and examines it critically. This discussion clearly establishes that there is a real phenomenon to be explained and that the explanation forces us to change our understanding of a number of basic biological processes. Much of the evidence examined is derived from studies of cell biology but increasingly it has become possible to examine the process at the molecular level. Studies of gene expression provide several promising perspectives on the process of transdifferentiation. Although this monograph focuses on some rather specialized experiments and discusses questions of definition, the phenomenon is so compelling and is of such fundamental importance that postgraduates and researchers in developmental and cell biology, as well as scientists in basic cancer and eye research, will find it equally interesting.