Hepatocyte nuclear factor 1 was identified as the transcription factor binding to a 20 bp (-150 to -131) region of the gene for human dipeptidyl peptidase IV, which has been shown to be important for the expression of dipeptidyl peptidase IV in the human intestinal and hepatic epithelial cell lines Caco-2 and HepG2. Functional analysis of the hepatocyte nuclear factor 1 site was performed with two minimal dipeptidyl peptidase IV promoter constructs (-250 to -41, and -150 to -41) with and without a 3 bp mutation in the hepatocyte nuclear factor 1 sequence, and used in transient transfection experiments with Caco-2 cells. The results show that the mutated constructs were able to drive transcription at only 5–10% of the activity of the non-mutated controls. Co-transfection of 3T3 cells with hepatocyte nuclear factor 1 (α or β) and dipeptidyl peptidase IV promoter constructs (-250 to -41 or -150 to -41) resulted in a 2.5–6-fold increase in transcription over controls with hepatocyte nuclear factor 1α but not with hepatocyte nuclear factor 1β. The results of this study show that hepatocyte nuclear factor 1 binds to the -150 to -131 region of the human dipeptidyl peptidase IV promoter and is necessary for transcriptional activation of the gene for dipeptidyl peptidase IV.