The nervous system is made up of several kinds of cells which should ideally be examined separately in biochemical studies. Since we are not yet able to isolate the different kinds of cells, use is made of cell lines derived from a single cell which are isolated from tumors of the nervous system and which can be reproduced at will in the same way as bacteria. They include cell lines isolated from a mouse neuroblastoma which exhibit some of the properties of nerve cells. Hybrid cells obtained by fusion of mouse neuroblastoma cells with rat glioma cells display even more characteristics of nerve cells. This article considers properties which justify our regarding the hybrid cells as neuron models. Application of the cells to problems of the nervous system is then demonstrated: 1) processing of information arriving in the form of mutually opposing hormonal signals; 2) mode of action of morphine.