Previous investigators have localized the human glial fibrillary acidic protein (GFAP) gene in the segment 17q21 in chromosome 17. In the present study, we statistically assessed the association between the allelic status in thirty-three microsatellite loci and the immunohistochemical expression of GFAP in twenty human astrocytic tumors. The results demonstrated that the loss of heterozygosity in only one locus (D17S795 located in 17q21.2) was significantly associated with the impaired expression of GFAP (P = 0.0280, Pc = 0.0384 by Fisher's exact test). The adjacent loci located in 17q21.1 and 17q21.3 were not relevant to GFAP expression. Those data suggest that the critical region responsible for GFAP expression (coding sequence and regulatory elements) is located close to the locus D17S795 in the segment 17q21.2.