The effects of sodium hypochlorite for the destruction of P. aeruginosa, E. coli, K. pneumonias and S. anreas and for the prevention of contamination of irrigation fluid, which is either exposed to ICU environment or used for cleansing oral or trachea catheter tips, were tested and the following results were obtained. 1) The sodium hypochlorite solution 1: 800 destroyed P. aeraginosa, E. coli, K. pneomoniue and S. aweas in 5 minutes. This bactericidal effect was observed to be retained after the solution had stood 24 hours. 2) Viable P. aeraginosa was not detected immediately, 5 minutes and 10 minutes after exposure to 1: 500, 1: 800 and 1: 1000 sodium hypochloride solutions respectively. 3) The sodium hypochlorite solution 1: 800 prevented contamination of the irrigation fluids during a 24 hour exposure to the ICU environment. 4) P. aeraginosa and other gram-negative bacilli were frequently isolated from the plain fluid used for irrigating and holding the suction tips which had been used for patients. However, no organisms were isolated from fluid containing sodium hypochlorite 1: 800 even after 24 hour usage. It is concluded that the use of fluid containing sodium hypochlorite for the irrigation of catheter tips can reduce development of infections in the ICU patients.