Of 611 prospectively studied patients in a surgical intensive care unit, 177 developed hospital infections (29%): urinary tract infections (37.2%), pneumonia (22.5%), sepsis (19.7%), wound infections (9.6%), etc. The commonest pathogens were Pseud. aeruginosa, E. coli, Staph. aureus, enterococci, Klebsiella pneumoniae and Proteus mirabilis. In preventing and combating hospital infections in intensive care units, priority should be given not to antibiotics but to hygiene in the hospital. Systemic antibiotic prophylaxis prevents neither hospital-contracted pneumonia, sepsis nor urinary tract infections. There is an urgent need for controlled studies on the necessity and selection of locally active antibacterial and antimycotic substances to prevent germ ascension in vein and bladder catheters.