E2FBP1, an ARID (AT-rich interaction domain) family protein, has been isolated as a protein that interacts with E2F-1, a member for the E2F family transcription factor. The closely related Bright binds to specific AT-rich DNA sequences and regulates B-cell-specific gene expression. Although Bright is specifically expressed in differentiating and matured B cells, E2FBP1 is expressed ubiquitously in a variety of tissues, suggesting that E2FBP1 plays a role in different biological processes. However, the function of E2FBP1 remains largely unknown. The present work showed that expression of E2FBP1 protein was up-regulated by forced expression of p53, and its expression levels were low, in tumor cells lacking wild-type p53. Furthermore, E2FBP1 levels were increased following DNA damage, in parallel with levels of p53 and p21 Waf1/Cip1. In addition, coimmunoprecipitation assays indicated that E2FBP1 could interact with p53 in vivo. These results suggest the possibility that E2FBP1 is involved in the p53 regulatory pathway.