Epidemiologic supervision of P. aeruginosa infections is a daily care for microbiologists. The aim of this study is to evaluate quantitative antibiogram, which compare strains by calculation of euclidian distances from inhibition zone diameters on agar, compared with pulse field gel electrophoresis (PFGE) results. 53 isolates of P. aeruginosa obtained from bronchial secretions of 26 patients in intensive care unit are typed by conventional disk diffusion test on agar with 11 usual antibiotics. Dendrogram of euclidian distances is performed by Taxotron computer program (P.A.D. Grimont, Institute Pasteur, Paris); results are compared with 53 PFGE patterns after restriction with Spe I (Genepath system, BIO-RAD). Quantitative antibiogram has a high discriminatory power for beta-lactamin resistant strains: 27 isolates from 11 patients clustered in 5 types where PFGE discerned 5 patterns. The discriminatory power is low for beta-lactamin sensible strains: 26 isolates from 15 patients clustered in 8 types where PFGE discerned 19 patterns, but serotyping method combined with quantitative antibiogram restore a high disriminatory power for beta-lactamin sensible strains.