The human cDNA probe pPGK824 , of Singer-Sam et al. [Singer-Sam, J., Simmer , R. L., Keith, D. H., Shively , L., Teplitz , M., Itakura , K., Gartler , S. M. & Riggs, A. D. (1983) Proc. Natl. Acad. Sci. USA 80, 802-806] was used to isolate a genomic clone lambda PGK-1 containing a portion of an autosomal locus for phosphoglycerate kinase (PGK). A unique sequence subclone (pGK-1) of lambda PGK-1 was then used to map this locus to the region p23-q12 of human autosome 6--i.e., to the interval that contains the major human histocompatibility locus (HLA). Since an autosomal gene coding for testis-specific PGK in the mouse has been shown to be closely linked to the H2 locus and to the T/t-complex locus [ Eicher , E. M., Cherry, M. & Flaherty , L. (1978) Mol. Gen. Genet. 158, 225-228], it is suggested that the lambda PGK-1 recombinant clone contains part of the human gene for the testis-specific isozyme of PGK. In addition, the subcloned pGK-1 detects an EcoRI restriction fragment length variant and may therefore prove useful for further genetical analysis of the HLA region and specifically for testing the hypothesis that spina bifida and anencephaly may be the human equivalent of the murine defects due to the T/t-complex locus. Our findings support the generally held hypothesis that a large number of structural loci clustered around the histocompatibility genes have been conserved in a close linkage association throughout a large evolutionary interval.