The aim of this research has been considering the increasing importance of hospital infections due to the so called "opportunist bacteria", to value which is the frequency of isolating Pseudomonas aeruginosa types from various hospital sections pathogenous material. Moreover morphological, straining, cultivation and biochemical characteristics have been studied together with enzymatic properties (lipase, ecc.), serological characteristics and sensitivity to antibiotics. We hoped to find same differences among Pseudomonas aeruginosa different types related to the pathological material kind or to the department of origin. The Pseudomonas aeruginosa different types have been isolated, mostly from urine and bronchial secretions belonging to patients in the Reanimation Department, with a somewhat low frequency (9.8%) in relation to the total number of types. Results obtained showed how all the types have almost the some characteristics and only seldom (8.3%) a complete resistance to all antibiotics tested. Most past of them (31.4%) instead showed sensibility to 4 or more different antibiotics.