The murine glial fibrillary acid protein (GFAP) gene is located on chromosome 11 in close proximity to the genes encoding transforming protein p53 (Trp53) and myeloperoxidase (Mpo). Both Trp53 and Mpo have been mapped to human chromosome 17, but the chromosomal assignment of human GFAP has not been previously determined. In this report, we have amplified a cDNA fragment encoding a portion of GFAP from human brain and have used this probe to screen a mouse x human somatic cell hybrid panel. The results show that a human-specific GFAP species of approx 3.7 kb maps to one of these lines, TMS5, which contains chromosome 17 as its only human chromosome. On the basis of these data we speculate that there may be evolutionary relatedness between GFAP and other genes that map to both murine chromosome 11 and human chromosome 17.