During normal development of the nervous system, up to 50 percent or more neuronal and glial cells die by programmed cell death. In the developing neuron, a continual access to neurotrophic factors is required for survival of the cells. The death may be a passive process, and the absence of neurotrophic factors leads to a loss of metabolic activity and, ultimately to cellular degeneration. Alternatively, apoptosis may be a metabolically active process and neurotrophic factors are necessary to repress the "suicide" response of the cell. The role of intracellular calcium, RNA-synthesis, protein synthesis a gene expression is discussed.