The purpose of this study was to identify the proper changing time of tracheal suction catheter by examining the microorganisms inside after used. The samples were the adult and the elderly patients who were in the intensive care unit of one university hospital in Korea from the early December, 2002 to the end of May 2003. Since the patients needed tracheal suction, sterile catheter including other equipments were used whenever tracheal suction provided, to the experimental group. The sterile catheter with others were provided when the catheter repeatedly used for four hours, to the comparative group. Research was permited by tile head of hospital administration, hospital nursing department, microbiology and intensive care unit. The main results of the study are as follows. 1) The demographic characteristics between the two groups present statistically no difference. 2) Even the experimental group showed various kinds of microorganisms, the numbers of the kinds and carriers of the microorganisms were less than those of the comparative group. 3) The mean numbers of the microorganisms between the two groups were significantly different, p < 0.05. This study results strongly emphasize the needs of using sterile catheter whenever a nurse suctions to keep patient's airway open.