The intracellular localization of a tetraphenylporphyrin bearing four long lipophilic alkyl chains in electrocytes from Psammobatis extenta(Rajidae) is described. In contrast to what is usually the case, this porphyrin derivative is localized in the electromotor nerves and the nuclear chromatin of the electrocytes. Both structures exhibited intense fluorescence, whereas, the mitochondria were only slightly fluorescent. These data are discussed in relation to electrocyte death in a weakly electric fish. Additionally, electron probe X-ray microanalysis suggests a migration of chloride and cationic ions, which might be implicated in chloride and cationic channel activation in the electrocyte. © 2004 The Royal Society of Chemistry and Owner Societies.