A 4.6-kb EcoRI/BglII fragment of Serratia liquefaciens genomic DNA has been sequenced and within this fragment the chiB gene has been identified and characterized. The chiB ORF encodes a polypeptide with a deduced molecular mass of 52-kDa and the translational product in vitro has chitinase, but not chitobiase activity. Alignment of the predicted Chib 499 amino acid sequence indicated a chitin-binding and a catalytic domain that shares homology to the chitinase family 18 domain, to the Chib polypeptide of Serratia marcescens QMB1466 (93.6%), a human chitinase and several bacterial chitinases. This chiB gene sequence transcription/translation in Escherichia coli may be blocked by a RNA folding mechanism thus controlling the chitin utilization regulon in S. liquefaciens.