Abstract: A targeted disruption of the NF1 gene in mice has been used to demonstrate that both neural crest- and placode-derived sensory neurons isolated from NF1(-/-) embryos develop, extend neurites, and survive in the absence of neurotrophins, whereas their wild-type counterparts die rapidly unless NGF or BDNF is added to the culture medium. Moreover, NF1 mutant sympathetic neurons survive for extended periods and acquire mature morphology in the presence of NGF-blocking antibodies. The discovery is useful in screening candidate substances for inhibition of neurofibromin action and in therapy for neurodegeneration due to disease or trauma.