(--)Deprenyl, a monoamine oxidase B (MAO B) inhibitor is known to upregulate activities of anti-oxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in brain dopaminergic regions. The drug is also the sole chemical which has been repeatedly shown to increase life spans of several animal species including rats, mice, hamsters and dogs. Further, the drug was recently found to enhance anti-oxidant enzyme activities not only in brain dopaminergic regions but also in extra-brain tissues such as the heart, kidneys, adrenal glands and the spleen. We and others have also observed mobilization of many humoral factors (interferone (INF)-gamma, tumor necrosis factor (TNF)-alpha, interleukine (IL)-1beta,2,6, trophic factors, etc.) and enhancement of natural killer (NK) cell functions by (-)deprenyl administration. An apparent extension of life spans of experimental animals reported in the past may be better explained by these new observations that (-)deprenyl upregulate SOD and CAT activities not only in the brain but also in extra-brain vital organs and involve anti-tumorigenic as well as immunomodulatory effect as well. These combined drug effects may lead to the protection of the homeostatic regulations of the neuro-immuno-endocrine axis of an organism against aging.