The p53-binding protein 2 (53BP2) was identified as a binding protein to a tumor suppressor p53. We examined the genetic aberrations of 53BP2 gene in various human cancer cell lines. Although no gross genomic alteration or mutation of 53BP2 gene was observed, 53BP2 mRNA levels were highly variable. There was no association between the 53BP2 mRNA level and the p53 status. When we examined sensitivities of these cell lines to DNA-damaging agents including UV irradiation, X-ray irradiation and cis-diamine-dichloroplatinum (CDDP), we found that higher 53BP2 mRNA expression was correlated with the sensitivity to these agents.