A large imprinted gene cluster in human chromosome 11p15.5 has been implicated in Beckwith-Wiedemann syndrome and Wilms' tumor. We have identified a paternally expressed imprinted gene, PEG8/IGF2AS, in this locus. It is transcribed in the opposite direction to the IGF2 transcripts and some genomic regions are shared with the IGF2 gene, as in the case of the mouse imprinted Igf2as gene reported previously by T. Moore et al. As to the relationship between these genomic regions, the human and mouse genes are very similar but there is no homology in their middle parts. Interestingly, PEG8/IGF2AS and IGF2 were found to be overexpressed in Wilms' tumor samples, at levels over ten and a hundred times higher than that in normal kidney tissues neighboring the tumors, respectively. These findings indicate that PEG8/IGF2AS is a good marker of Wilms' tumor and also suggest the possibility of PEG8/IGF2AS being one of the candidate Wilms' tumor genes.