The bacillus pyocyanic, isolated in 1882 by Gessard, was not at the origin of infections except in cases of seriously ill patients or in the premature babies with diminished resistance. After the discovery of antibiotics and their excessive use in therapy, resistent strains of bacillus pyocyanic have been developped leading to infections in which the frequency and seriousness are still increasing. The medical staff neglecting the antiseptic measures during operations and dressings of the wounds, are at the origin of the epidemies in the hospitals. Because of its enzymatic power the bacillus pyocyanic may develop in a solution of penicillin, anesthesics, antiseptics or in the material or instruments unproperly sterilized. It is therefore necessary that severe prophylactic measures must be taken in addition to antibiotic treatment. The most active of the antibiotic therapy are the following: colimycin, polimyxin, gentamycin and carbenicillin. 46 cases of bacillies pyocyanic infections have been treated by colimycin at the ORL Clinic of Geneva and in 67.3% of cases, this treatment sterilized the infected areas. The cases resistent to colimycin were then treated by gentamycin, without favorable results. On the other hand, two cases of bacillus pyocyanic resistent to the previous antibiotics were treated with success by carbenicillin.