We observed two episodes of Pseudomonas aeruginosa colonisation taking place in a Hospital. This organism was isolated in a pure culture from the faeces of 41 newborn children, many patients and from a large part on the obstetrics and pediatry division's staff. The AA. investigated the ways of spreading of this germ which caused both in the adults and the babies, no sign of illness. Biotypes one causing the first episode and the other related to the second one were isolated them showed a wide spectrum of resistance to several antibiotics and they of disappeared after accurate measures of hygiene concerning persons and places were adopted.