Idiopathic peripheral neuropathy is common and likely due to genetic factors that are not detectable using standard linkage analysis. We initiated a candidate gene approach to study the genetic influence of the small heat shock protein (sHSP) gene family on an axonal motor and motor/sensory neuropathy patient population. The promoter region and all exonic and intronic sequences of the 10 sHSP genes (HSPB1-HSPB10) were screened in a cohort of presumed nonacquired, axonal motor and motor/sensory neuropathy patients seen at the Ohio State University Neuromuscular Clinic. A missense mutation in the gene encoding small heat shock protein B3 (HSPB3, also called HSP27, protein 3) was discovered in 2 siblings with an asymmetric axonal motor neuropathy. Electrophysiologic studies revealed an axonal, predominantly motor, length-dependent neuropathy. The mutation, HSPB3(R7S), is located in the N-terminal domain and involves the loss of a conserved arginine. The discovery of an HSPB3 mutation associated with an axonal motor neuropathy using a candidate gene approach supports the notion that the small heat shock protein gene family coordinately plays an important role in motor neuron viability.