Ishikawa et al (2008) reported complex I deficiency caused by mutations in the ND6 gene of complex I in non-oncocytic mouse lung tumours. Interestingly, these mutations increased the metastatic potential of the tumours (Ishikawa et al, 2008), whereas complex I deficiency in oxyphilic tumours does not seem to be associated with metastasis. The gene discussed is MT-ND6; the disease is neoplasm.