The cGMP signalling pathway has been suggested to be involved in the signal transduction of various physiological functions in insects; olfaction, antidiuresis and eclosion. However, the cGMP signalling mechanism has remained elusive. We isolated two cDNAs of the cGMP dependent protein kinase, designated BmPKG-Ialpha and BmPKG-Ibeta. The deduced amino acid sequences indicate that both BmPKG-Ialpha and BmPKG-Ibeta appear to consist of an amino terminal region, a cGMP binding domain and a protein kinase domain. Transcripts of BmPKG-Ialpha and BmPKG-Ibeta were detected in various tissues: flight muscles, antennae, midgut, legs, head, thoracic ganglia and Malphighian tubules. Recombinant BmPKG-Ialpha bound to lipid membranes, while BmPKG-Ialpha with a deleted amino terminal region failed to bind to lipid membranes.