Based on our earlier studies of the natriuretic peptide gene expression in cardiac cells we now have constructed several hybrid gene constructs containing elements of the rat B-type natriuretic peptide gene and salmon cardiac peptide (sCP) gene 5'promoter areas. The gene promoter of the sCP drives luciferase gene expression very effectively in rat cardiac atrial cells but not in ventricular cells. At -80 and -91 in the rat BNP promoter there are GATA elements important in both the basal and mechanical stretch-induced activation of the BNP promoter and at -495 there is an Ets-binding element (EBS) inducible by endothelin-1 (ET-1). In the hybrid gene constructs we have inserted the GATA-containing BNP proximal promoter with the distal sCP gene promoter and also the other way around, that is, we have inserted the BNP GATA and EBS areas in front of the sCP gene proximal promoter. We have transfected all these gene constructs in rat cardiac cells and studied the activity of the mixed promoters in basal and hypertrophic conditions. It seems that the placing of the elements and also the sequence in their surroundings have an effect on the activity. The BNP GATA sites inserted in the proximal area function more effectively (at least several tens of times) than the same elements inserted in front of the sCP gene. Our results suggest that the induction of the GATA and EBS by mechanical stretch of the myocytes or by ET-1 is partly dependent on the placement and the surrounding sequences of these transcription factor binding sites.