Cultured neurons of the mammalian dorsal root ganglia (DRG) can be divided, as in intact ganglia, into two classes: 'large light' (neurofilament-positive) and 'small dark' (neurofilament-negative) neurons. While 'small dark' neuron survival depends on NGF during ontogenesis, little is known about the neurotrophic factor requirement of the 'large light' sub-population. This study demonstrates that the in vitro survival of neonatal mammalian neurofilament-positive DRG neurons requires the presence of a neurotrophic factor present in skeletal muscle extract.