This study is to evaluate contamination of the 3-way stopcocks connected to infusion set, which is used to the patients admitted to emergency room in a general hospital in D city. The data were collected from Oct. 1, 2001 to Feb. 25, 2002. First of all, in order to select microorganisms, From the 50 patients were randomized, Coagulase Negative Staphylococcus, Staphylococcus aureus, micrococcus, Pseudomonas aeruginosa, Acinetobacter detected. Coagulase Negative Staphylococcus, Staphylococcus aureus, micrococcus were determined to be evaluated in this study. As a result, 8 of the patients were Coagulase Negative Staphylococcus positive(> 15 colonies), 4 were Staphylococcus aureus positive(>15 colonies), 1 was micrococcus positive(>15 colonies). Among the patients who were Coagulase Negative Staphylococcus positive, 112(average) colonies were detected on the first day, 429 were on the second day, and 563 were on the third day. In case of patients of Staphylococcus aureus positive, 85(average) colonies were detected on the first day, 151 were on the second day, and the 203 were on the third day. CNS was cultured using API kit for the 8 patients who were in CNS positive. One case was detected Staphylococcus capitis, another one case was Staphylococcus chromogenes. Two cases were Staphylococcus xylosus, another two were Staphylococcus hominis, and the remainer were Staphylococcus epidermidis. As a result, the API codes of two Staphylococcus epidermidis had shown the same pattern, and the resistance patterns of the them were the same, too. As a result of resistance test among 5 patients who have shown that the same resistance pattern in 02SAK1, 02SAK5, 02SAK2, 02SAK4. As a result of this study, aseptic technique of 3-way stopcock intravenous therapy can protect infections, and it is needed the sterilization of the 3-way stopcock just before injection using disinfectants. It needs to improve the 3 way stopcock change intervals from 48 hours.