An endemic hospital infection caused by E. coli 0111:B4 together with Pseudomonas aeruginosa was observed in a county hospital over the period October 1973 till January 1974, which could not be brought under control by routine preventive measures against cross-infections established on the wards. By hospital sanitary examinations the waste water in the sinks and the hand-basins in some rooms of the newborn nursing wards were identified as sources. Their elimination by taking apart the sinks and placing the detached parts in 4% formalin solution for 2 hours, as well as disinfecting the basins also with a 4% formalin solution for 24 hours terminated the hospital infection. Some sporadic carriers of E. coli 0111:B4 among the newborn infants of the involved wards had been previously identified and could also be traced subsequently; hence, it may be concluded that the introduction of E. coli 0111:B4, which seems to be endemic in Vorarlberg, was due to patients or personnel. Voluntary submission to control investigations of the stool and appropirate treatment of the entire staff, involved in the infection, with strict routine surveillance of hand disinfection prior to washing seem to be justified by the successful results of these procedures. High risk of infection in newborn infants and babies, the special situation of an intensive care unit, as well as the combined appearance of Pseudomonas aeruginosa and enteritis coli from a source as an additional complication were the causes of this hospital infection.