Bestatin, the dipeptide N-[(2S, 3R)-3-amino-2-hydroxy-4-phenyl butanyl) l-leucine is a leucine aminopeptidase and aminopeptidase-B inhibitor. It exerts a direct stimulating effect on lymphocytes (and monocytes) via its fixation on cell surface leucinc-aminopeptidase, and an indirect effect on monocytes (and lymphocytes) via aminopeptidase B inhibition of tuftsin catabolism. Thus it is an immuno-modifier as shown by the Japanese and also our groups: a) immunomodifier, especially slimulator, in normal young mice; b) immunorestorator and spontaneous tumor preventive agent in aged mice: c) immunorestorator in the elderly and in cancer patients and HIV infected subjects. It stimulates granulocytopoiesis and thrombocytopoiesis in vitro, and can restore them in vivo in myelo-hypoplastic man. The anti-aminopeptidase action of Bestatin also protects enkephalins againt their catabolism, which encouraged us, with good preliminary results, to study its analgesic action and search for a preventive effect on “desaddicted” toxicomaniac relapses.

Bestatin/anti-aminopeptidase/pharmacological action