This study investigated the influence of chronically administered L-deprenyl on normal ageing-related parameters: multiple unit action potentials, the activities of the enzymes Na(+),K(+)-adenosine triphosphatase, glutathione-s-transferase and glutathione peroxidase, and the levels of lipid peroxidation products and lipofuscin contents in the brain regions (cerebral cortex, hippocampus, striatum and thalamus) of 24-month-old rats. The drug increased the activity of Na(+),K(+)-ATPase and glutathione-s-transferase. The activity of glutathione peroxidase remained unaffected. The drug also increased the multiple unit action potentials activity. The levels of lipid peroxidation products were, however, decreased, and lipofuscin accumulation was diminished by the drug. The results essentially indicated that chronic treatment of rats with L-deprenyl significantly influenced the ageing-related alterations in: multiple unit action potentials, Na(+),K(+)-adenosine triphosphatase, glutathione-s-transferase, lipid peroxidation products and lipofuscin accumulation. These novel data on the effect of L-deprenyl on parameters of normal ageing provide new additional evidence concerning the anti-ageing therapeutic potential of L-deprenyl.