One aspect of cell differentiation is the elaboration of morphology characteristic for each cell type. The wide variety of morphologies displayed by cells of different organs arises by a concerted sequence of changes in cell structures as the symmetrical, spherical process is, in a sense, reversed during malignant transformation, and cancer cells typically have lost their asymmetry. The purpose of our work is to understand the underlying mechanisms by which these events occur. We have developed an experimental system which permits us to detect, manipulate, and analyze cellular determinants of detailed cell shape. Neuroblastoma cells, grown in culture, can be induced to extend neurites, and to mimic the large range of morphologies elaborated by neurons in vivo. The general characteristics of neuronal morphology are carried in the genome, but we have shown that information which specifies the detailed shape of an individual cell can be carried in the cytoplasm. We are investigating where that information is carried in the cell, how it is transmitted to the cell, and how it is expressed.