The effects of peripheral benzodiazepines on the respiration of a neuronal cell, the mouse C 1300 neuroblastoma, were analyzed. The presence of 'peripheral receptors' to the [3H]PK 11195 ligand was checked in these cells. A dose-dependent decrease of the O2 consumption in the presence of Ro 5-4864 and PK 11195 was observed at concentrations consistent with a receptor-mediated action. Diazepam, clonazepam and Ro 15-1788 were inactive. Previous studies have localized the peripheral benzodiazepine receptors on the mitochondrial outer membrane. We report here an effect of the peripheral ligand on mitochondrial metabolism.