Hereditary motor and sensory neuropathy with focally folded myelin sheaths, or Charcot-Marie-Tooth disease neuropathy type 4B (CMT4B), is a distinct clinical and genetic entity belonging to the heterogeneous group of autosomal recessive demyelinating neuropathies. We previously described a large pedigree with CMT4B and found evidence of linkage to chromosome 11q23. We now describe a second, unrelated family in which two individuals were affected with CMT4B. We exclude the disease locus segregating in this smaller pedigree from the 11q23 region as well as from most of the regions where other CMT loci have been mapped. We thus provide evidence for a second locus causing the CMT4B phenotype.