The neurotoxic organochlorine insecticide chlordecone (Kepone) was examined in severalin vitroandin vivoneurochemical systems in an attempt to identify neuro‐chemical alterations that might be relevant to the central nervous system manifestations of chlordecone toxicity in humans.In vitro, chlordecone was a remarkably potent inhibitor of brain mitochondrial oxidative phosphorylation and associated Ca2+transport (Ki= 10−7M). At a high concentration of chlordecone (10−5M), destabilization of biological membranes was observed. Both of these effects appeared to contribute to inhibition of synaptosomal Ca2+uptake, which was accompanied by a pronounced, although paradoxical, stimulation of neurotransmitter release. Studies of the disposition of [14C]chlordecone revealed that the concentrations that elicited neurochemical changesin vitrowere comparable to the brain tissue chlordecone concentrations achieved with a 40 mg/kg tremorigenic dose in intact animals. However, no neurochemical correlates of chlordecone toxicity were observed in studies of dopamine and norepinephrine turnover in chlordecone‐intoxicated animals. These findings are discussed in relation to the development of neurochemical assays appropriate for investigating neurotoxic agents.