Poly[adenosine diphosphate (ADP)-ribose] polymerase (PARP), which is mainly located in the nucleus, catalyzes poly-ADP-ribosylation, and is associated with a variety of biological events such as DNA repair, cell proliferation and malignant transformation. The aim of this study was, using biopsy samples obtained under sonographic guidance, to assess whether PARP expression is altered in human hepatocellular carcinoma (HCC), and also to analyze the correlation between the expression of PARP and the patients' clinicopathologic features. Tumor and non-tumor specimens were obtained from a total of 27 HCC patients by percutaneous biopsy under sonographic guidance. Using homogenates of these samples, the expression of PARP in HCC was evaluated by Western blotting and compared with the patients' clinicopathologic features. Western blot analysis, using a total of 29 HCC and 27 non-tumor specimens, revealed that the expression of PARP was significantly increased in HCC compared with the non-tumor portions (p<0.01), and was greater in moderately differentiated HCC than in well differentiated HCC (p<0.05). The expression of PARP in HCC was increased in cirrhotic patients and tended to be greater in less differentiated tumors.