The effects of acute administration of maneb (30 mg/kg, i.p.), an agricultural fungicide, combined with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP 50 mg/kg, i.p.), a dopaminergic neurotoxin, were examined on mouse locomotor activity and catalepsy test. The pretreatment with maneb significantly exacerbated the effects of MPTP on locomotion and catalepsy in mice. These results suggest that exposure to some pesticides might enhance motor dysfunction.