The developmental loss of neurons in sympathetic, sensory, and some parasympathetic ganglia in familial dysautonomia suggests an inherited defect in the action of beta-nerve growth factor (beta-NGF). The role of this growth factor in dysautonomia has been difficult to resolve as there is no known source of authentic human beta-NGF. The availability of a cloned DNA probe for the human beta-NGF gene has allowed identification of some copies of the gene (alleles) in six affected families. Alleles differ in the length of restriction endonuclease fragments that hybridize to DNA probes for the gene. In two families, affected children did not inherit the same two alleles at the beta-NGF locus. Since this disease is transmitted in an autosomal recessive manner, affected children must share the same alleles at the locus causing the disease. This analysis excludes the beta-NGF gene region as the cause of this neurologic disease but does not eliminate other genes involved in beta-NGF action, such as those coding for processing enzymes, receptors, or other subunits of the NGF complex.