The behavioural and electrocortical effects of paraquat were studied after its administration into the substantia nigra, pars compacta, an area where dopamine-(DA) containing cell bodies are present, into the caudate nucleus, where DA-containing nerve endings of the DA nigro-striatal system project, into the locus coeruleus, an area containing noradrenaline cell-bodies and into the n. raphe dorsalis or into the n. raphe medianus, two nuclei containing serotonin (5-HT) cell bodies. The intraventricular administration of paraquat (10 and 50 micrograms) produced an intense pattern of behavioural stimulation and an increase in locomotor activity, circling and the wet-dog syndrome. This symptomatology was accompanied by desynchronization of the electrocorticogram (ECoG) and the appearance of bilateral high voltage epileptogenic spikes, culminating in clonic convulsions. The infusion of paraquat into the s. nigra produced contralateral head and neck deviation, behavioural and motor stimulation, these effects being observed also with smaller doses (1 and 5 micrograms), than those used intraventricularly. The ECoG activity was desynchronized and characterized by high voltage spike discharges. A similar behavioural, postural and ECoG pattern was also observed after infusion of paraquat into the caudate nucleus (10, 25 and 50 micrograms). In addition, paraquat, infused into the locus coeruleus or into the raphe nuclei (5 and 10 micrograms), produced circling, escape responses, jumping and clonic convulsions accompanied by ECoG desynchronization and epileptic phenomena. In conclusion, the present experiments showed that paraquat was able to produce central neurotoxicological effects which did not seem to be specific, at least for the doses used, for the DA nigro-striatal system.