A family of growth arrest specific (Gas) genes was operationally defined on the basis of the strategy utilized to isolate them e.g. differential expression in quiescent and growing cells. Our interest in the Gas-3 gene was prompted by our previously reported localization of the gene on the mouse chromosome 11.44 +/- 1.9 cM proximal to the Trp53 locus and by the finding, by others, that it codes for a myelin protein and that a point mutation in its fourth putative transmembrane region is associated with the trembler mutation. We have isolated the human homologous of the mouse Gas-3 gene and utilized the cloned sequences as a probe to localize the gene on human chromosomes both by analysis of human-rodent somatic cell hybrids and in situ hybridization of human metaphases. We have now localized the human Gas-3 gene on chromosome 17p12-13. Its possible role in both the development of neoplasia in neurofibromatosis patients and in the myelin degenerative disease as the Charcot-Marie-Tooth is discussed.