Using clonal cell lines isolated from murine neuroblastoma C1300, we investigated the mitochondrial changes related to neuronal differentiation and, more generally, the role played by the mitochondrion in this phenomenon. By different approaches (measurement of the mitochondrial mass, immunoquantification of specific mitochondrial proteins, or incorporation of Rhodamine 123), the differentiation of the inducible clone, N1E-115, was found associated with an important increase of the cellular content in mitochondria. This increase could be observed with differentiating N1E-115 cells maintained in suspension, i.e. under conditions where neurite outgrowth is prevented but other early stages of (biochemical) differentiation continue to occur. That these mitochondrial changes are likely to be correlated with these stages of neuronal differentiation, rather than with simple progression to the postmitotic stage, stems from comparative experiments with clone N1A-103, a neuroblastoma cell line variant that becomes postmitotic after induction but fails to differentiate and shows no modification in its cellular content in mitochondria. In accordance with these observations, chloramphenicol prevents differentiation when added together with the inducer. This effect is probably related to the inhibition of mitochondrial translation rather than to modification of the bioenergetic needs because oligomycine, a potent inhibitor of the mitochondrial ATP synthetase, shows no effect on neurogenesis. As a working hypothesis and in keeping with independently published models, we postulate that products resulting from mitochondrial translation could be involved in the organization of the cytoskeleton or of certain membrane components whose rearrangements should be the prerequisite or the correlates to early stages of neuronal differentiation.