c-Jun N-terminal kinase (JNK)-interacting protein 1 (JIP-1) is an important scaffolding protein in the JNK signalling pathway. It is also believed to play a role in the mediation of mitogenic messages from the plasma membrane to the cell interior. Previous studies have suggested that the JIP gene is co-regulated with the insulin-like growth factor II (IGF-II) gene, thereby contributing to the growth stimulatory effects of this potent growth factor. The striking co-expression of these two genes has been found in murine foetuses as well as in primary human embryonic tumours. When six primary Wilms tumours (nephroblastomas) from pig were examined, the two genes showed a high degree of co-variation in the sense that high or low expression of IGF-II and high or low expression of JIP-1 ocurred together. By contrast the expression of a third Wilms tumour-related gene, WT1, was completely uncorrelated to the expression of IGF-II and JIP. In this respect, porcine nephroblastomas resemble human Wilms tumours. This further suggests that JIP-1 may play a role in the regulation of IGF-II-driven tumour cell proliferation.