Nerve growth factor (NGF) influences the survival and differentiation of a variety of neuronal and nonneuronal cells. The actions of this polypeptide result from binding to specific cell surface receptors which are present as both high and low affinity sites. Although both types of receptor bind NGF only the high affinity form is capable of signal transduction. NGF exhibits nerve growth stimulating activity and is involved in the regulation of growth and the differentiation of sympathetic and certain sensory neurons. Further, NGF stimulates division and differentiation of sympathetic and embryonic sensory neurons.