Having previously reported a high frequency of increased STAT3 activation in RCC, especially in metastatic disease (Horiguchi et al, 2002b), we thought that STAT3 could be a novel therapeutic target for RCC and, in this study, examined whether the STAT3 inhibitor WP1066 shows antitumour activity against RCC in vitro and in vivo. Here, STAT3 is linked to renal cell carcinoma.