Survey of resistance of beta-lactam's resistance of P. aeruginosa have to be conducted. 410 strains of P. aeruginosa ticarcilline resistant have been studied. 52% of these strains were cephalosporinase producing alone or in combination with penicillinase. beta-lactam's inhibitors are not fully efficient upon these strains. Upon cephalosporinase producing strains bactericidal activity of C3G is difficult to obtain. At low concentration selection of strains with upper MICs is observed. This phenomenon is not observed at high concentration of antibiotics. Cefepime show a good bactericidal activity against P. aeruginosa.