The 5'-flanking region of the gene encoding human muscle glycogen synthase was isolated from a human placental genomic library and sequenced. The sequence is TATA-less and G+C-rich, and putative transcription-controlling sequences were identified. Furthermore, a simple (dC-dA)(n) sequence repeat was identified about 4 kb upstream from the start codon. This sequence was highly polymorphic and five alleles were typed in the Japanese population using the polymerase chain reaction.