Diabetes and aging share some common mechanisms in their pathogenesis and diabetics are more prone to diseases of the elderly. Seeking for therapies likely to be proposed in the synchronised treatment of aging and diabetes is of great interest and l-deprenyl, a selective monoamine oxidase (MAO-B) inhibitor, is a possible candidate with its antioxidant, antiapoptotic and neuroprotective properties. Tissue MAO, NO and mRNA expression of nitric oxide (NO) synthase (NOS) isoforms were assessed in streptozotocin (STZ)-induced diabetic rats to evaluate the effect of l-deprenyl treatment. Twelve weeks of treatment had no significant effect on NO levels. Four-weeks treatment decreased tissue MAO activities and caused a decrease in expression of NOS-2 and NOS-3 in heart tissue of both controls and diabetics, and a decrease of liver NOS-3 expression in controls (p < 0.05). l-Deprenyl, causing a decrease in tissue NOS expressions, might be of benefit by protecting the organism from the toxic radical effects of NO.