The homologue of the rat pancreatic elastase I gene was found in the human genome, but its transcription was completely suppressed in the adult human pancreas as we reported previously. In this study, we characterized the complete structure of the eight putative exons of the silent gene for human elastase I. A genotype analysis of the exon 1 DNA sequence revealed that at least two allelic elastase I genes are present in human genomes. A primate-specific repetitive DNA element (MER1) was identified in the 3'-flanking region of the human elastase I gene. The primary structure of human preproelastase I, deduced from the sequences of the eight exons, showed an 89% identity with that of porcine or rat pancreatic preproelastase I. The amino acid residues of the serine protease catalytic triad and the eight cysteine residues conserved in the elastase family were present at positions equivalent to those observed in porcine and rat elastase I, suggesting that the gene product may function as an elastolytic enzyme if this gene is expressed in any tissue.