In vivo effects of diethylhydroxylamine (DEHA) on lipid peroxidation and lipofuscin formation in the nervous tissues of rat have been investigated. Rats were fed DEHA for 30, 60 and 90 days and lipid peroxidation levels and lipofuscin concentration measured in cerebellum, brain stem and spinal cord. Lipofuscin contents were also assessed histochemically. The results showed that the drug caused a significant reduction in lipid peroxidation level and lipofuscin concentration related to ageing.