Systemic toxicity of p,p'-DDE (DDE) in aged male rats was investigated in Wistar rats by oral administration of DDE. About 10 mg/kg DDE had been daily administered for 28 days from 48 weeks to 52 weeks of age and its effects were observed subsequently. The administration of DDE did not give rise to any overt signs of toxicity. Male reproductive organs were not affected and serum biochemistry was not impaired at the dose of this experiment. Organ weights of the liver and spleen slightly increased and the thymus weight reduced with DDE administration. Serum total cholesterol and free T4 levels slightly decreased with DDE administration, albeit statistically insignificant. Our results indicated that even aged male rats were resistant to DDE exposure at the daily dose of ca. 10 mg/kg. However, metabolic and immunological changes still remained uncertain. Further investigation should be performed to reveal the entire effects of DDE on aged male rats.