Leech therapy is a very old treatment which was very used in Europe untill XIX century, specially for arthritic and arthrosic conditions, and for dyscrasia too. In this century leech therapy has recovered significance after discovery of hirudine, the active substance of the leech. New applications are object now of researchers, specially in Germany; leech therapy is applied in mycrocirugy, for stopping haemorrhages, in amputations, in pain in extremities for obstruction of blood circulation, etc. Application of leech therapy may produce a microbiological contamination for Aeromonas hydrophila, which is well treated with cephalosporin third or first generation. The author directed a comparative work of research employing leech therapy and electrotherapy (tens) in painful gonarthrosis