Arising from: J. E. Kokoszka et al. Nature427, 461–464 (2004) The ADP/ATP translocator (or adenine nucleotide translocase; ANT) is thought to play a dual role: in the transport of ADP and ATP across the mitochondrial inner membrane and in the formation of the mitochondrial permeability-transition pore (mtPTP), a nonspecific pore that is an important mediator of apoptosis (programmed cell death)^,,. However, Kokoszka et al. have shown that mitochondria from livers of ‘ANT-knockout’ mice, in which the ANT has been genetically inactivated, still possess mtPTP activity. From this, the authors conclude that the ANT is a non-essential component of the mtPTP that may be dispensable for mtPTP-associated cell death. These results, which contradict previous evidence^, and cast doubt on a widely accepted model for the mtPTP (ref. ), warrant scrutiny and call for a fundamental reappraisal of the role of the ANT in liver metabolism.