The 5'-flanking region of the rat thrombomodulin gene was cloned by polymerase chain reaction (PCR) amplification of adaptor-ligated rat genomic DNA fragment libraries, using primers derived from the coding sequences of the thrombomodulin cDNA and adaptor primers. By sequence analysis putative regulatory elements in the promoter domain were shown to include a TATA box and several conserved binding sites for stimulatory protein 1 (SP1) and activator protein 2 (AP2). The transcription factor activator protein 1 (AP1) binding site located in the 5'-flanking region may serve as a negative gene regulatory site for tumor necrosis factor-alpha (TNF-alpha). A potential retinoic acid response element (RARE) and a possible cAMP response element are located in the putative promoter region, suggesting a role for retinoic acid and cAMP in the induction of thrombomodulin gene expression. The rat thrombomodulin gene promoter sequence shows 89% homology to that of mouse and 77% homology to that of human.