The effects of different types of pesticides on the in vivo striatal dopamine release were investigated by using in vivo brain microdialysis technique. MPTP, paraquat, maneb, dicofol, DDT, lindane and flutriafol (1 mM) were administered directly into the striatum, and levels of dopamine and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) were measured using HPLC-EC. Intrastriatal administration of pesticides induced the following maximal effects on the dopamine levels: maneb 791 +/- 87%, dicofol 101 +/- 1%, DDT 779 +/- 32%, paraquat 956 +/- 80%, lindane 281 +/- 28% and flutriafol 218 +/- 51% with respect to basal levels. Infusion of pesticides also produced alterations in extracellular DOPAC and HVA levels. A comparative scale of potency was developed to estimate the relative potency of pesticides to induce striatal dopamine release in vivo, using the same concentration and experimental conditions. According to this comparative scale of potency, paraquat is 10 times more potent (in a scale of 10) than dicofol, which did not induce any effect on dopamine release. The second more potent pesticide is maneb, followed by DDT, the organochlorine which has the highest potential to produce alterations on dopaminergic neurotransmission; flutriafol and the organochlorine lindane produced moderate increases in dopamine levels. These results suggest that different classes of pesticides, with different structures and biochemical activities, may affect the striatal dopaminergic system differently, inducing neurotoxicity.