The cDNA for human liver glycogen synthase was isolated by screening a human liver cDNA library constructed in λgt11. The full cDNA was 2912 bp in length. It coded for a protein of 703 amino acid residues with a molecular mass of 80.9 kDa. The number of amino acids was identical to and the deduced amino acid sequence homology was 92% that of the rat liver enzyme. The human and rat liver glycogen synthases are truncated by 34 amino acids compared to the human muscle enzyme, and by 32 amino acids compared to the rabbit muscle enzyme. The amino acid similarity between human liver and human muscle glycogen synthase was only 69%. It was least similar in the N and C terminal regions of the molecule. Two highly conserved regions are present in all published amino acid sequences for glycogen synthase, including those of the two yeast enzymes. These regions include the amino acid sequences from 201 to 400 and 501 to 600. This high conservation suggests that the catalytic site and the glucose-6-P and nucleotide allosteric sites are included in these regions.