In the current study the influence of single compounds and concurrent exposure to popular insecticides: organophosphate (OP) – chlorpyrifos (CPF) and synthetic pyrethroid (PYR ) – α-cypermethrin (CM) on some oxidative stress parameters and cholinesterase (ChE) activity in rats was investigated. Animals received by gavage 10 mg of single compounds or 5 mg of each per kg bw daily in rapeseed oil for 14 and 28 days. Concentrations of total thiols and TBAR S, activity of catalase and cholinesterase were measured in tissues. Total thiol concentrations declined in plasma in all experimental groups after 14 and 28 days, while in liver a decrease was noted after only 14 days in animals receiving CPF and after 28 days in rats treated with CM alone with a mixture of pesticides. Lipid peroxidation presented as TBAR S concentration was elevated mostly after 2 weeks of exposure in brain and liver but not in plasma in all experimental groups. Catalase activity increased in erythrocytes in all groups treated with insecticides, while in liver CM administered alone reduced the activity of the enzyme.Cholinesterase was markedly depressed to a different degree in plasma and brain of animals receiving CPF alone or in combination, while CM did not significantly elevate brain ChE. The results of this study seem to indicate that CM and CPF apart from known modes of action demonstrate their toxicity also through free radical mediated mechanisms. It is also evident that CM administered with CPF does not affect the cholinesterase inhibition generated by the latter.