We have determined the sequence of an 812-bp BamHI-EcoRI restriction fragment containing the 5' region of the human gene for PGK (3-phosphoglycerate kinase or ATP:3-phospho-D-glycerate 1-phosphotransferase; EC 2.7.2.3). The fragment contains 450 bp 5' to three start points for transcription (located by primer extension and S1 nuclease mapping), a leader sequence 85-94 bp long, the first exon of gene (65 bp), and part of the first intron. The promoter region is extremely G + C-rich, lacks a TATA box, and has an 8-bp direct repeat. A comparison of the promoter region for PGK with other promoters on the X-chromosome reveals homology with the promoter for HPRT, but not with the operator for factor IX.