Thrombin-activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like pro-enzyme that, once activated, attenuates fibrinolysis. Little is presently known of the factors that regulate expression of CPB2, the gene encoding TAFI. This study identified 10 potential transcription factor binding sites (denoted A-J) within the proximal promoter region of CPB2, spanning nucleotides -425 to +21; two of these represent previously-described binding sites for CCAAT/enhancer binding protein and glucocorticoid receptor. We identified additional transcription factors that bind within the proximal CPB2 promoter, namely, nuclear factor-Y (NF-Y) and hepatocyte nuclear factor-1alpha (HNF-1alpha). Binding of NF-Y to the region between nucleotides -76 to -59 (Site B) is important for basal CPB2 promoter activity; NF-Y may be a key factor for the recruitment of the transcriptional machinery to the TAFI gene promoter. HNF-1alpha binds at the interface between Sites C and B. Transient transfections of CPB2 promoter-reporter constructs showed that HNF-1alpha binding is essential for the activity of this promoter in HepG2 cells, indicating that HNF-1alpha is involved in the liver-specific expression of CPB2.