CRE-BP1 is a transcriptional regulator binding to the cyclic AMP response element (CRE). To understand the role of CRE-BP1 in vivo, we studied the expression of the CRE-BP1 gene in monkey tissues including the central nervous system, in rat regenerating liver, and in human cancer tissues compared with normal tissues. The CRE-BP1 mRNA was detected in all tissues examined, and was fairly abundant in brain. The CRE-BP1 mRNA was expressed in monkey brain tissues with different region specificities. In the hippocampus, frontal lobe, and parietal lobe, the CRE-BP1 mRNA was abundant and two mRNA species 4.0 kb and 3.7 kb in length were expressed. In rat liver, the expression of the CRE-BP1 gene was increased up to 4- to 5-fold of the normal level within 12-24 h after partial hepatectomy. Furthermore, the levels of CRE-BP1 mRNA in some clinical samples of human tumors were apparently higher than that in normal tissues. These results suggest that CRE-BP1 may be important for both the signal transduction in brain and cellular proliferation.