The structure of the human glucagon gene and the sequence around the putative promoter region and transcriptional start site are shown. Cloning and sequencing of the cDNAs, coding for preproglucagon from human pancreas and colon, as well as primer extension analysis of RNA from pancreas, ileum and colon point to an identical transcriptional start site in all tissues, about 3 X 10(3) base pairs upstream from the first coding exon as defined by Bell et al.