Post-operative wound infections have been the serious problems in nursing care in the operating room and appear to be strongly related to the infection occurring during the operation. The purpose of this study is to identify the level of contamination in saline used in the operation and also examine the correlation between the contaminated saline and the length of the operation, and unclean atmospheric factor. Subjects for this study include 13 cases of operation performed at the operative theatre of a hospital in Seoul area. Test samples and related data were collected from this medical facility between Oct. 6 through Dec. 10, 1994 by the auther and a nurse who worked in the operating room. For the study, multiple batches of saline sample were collected at the various time intervals during the operation and filtered through the membrane filters. Viable microorganisms retained on the filters were cultured on the appropriate culture media and the levels of existing cells in saline were enumerated according to Koch's method. In the analyses of the data, Pearson's correlation coefficient was obtained for the examination of relationship between the length of operation and numbers of microorganisms existing in saline and for the comparison of the differences in numbers if microrganisms in saline sample collected at the various operative stages, e. g. pre-incision, excision and skin suturing stages, ANOVA and Scheffe Tests were performed. The results of this study are summarized as follows. 1) The lenth of the operation and numbers of microorganisms in the saline used in the operation appeared to be significantly correlated (r =0.5467, P<0.001). 2) In case of saline exposed to air, but not used in the operation, the length of exposure to the air and the numbers of microorganisms present in saline also showed an apparent correlation(r=0.5087, P<0. 001). 3) The frequencies of occurrence of microorganisms in saline used in the operation and in saline exposed only to the air in the given time showed significant differences(t=3.73, p=.0000). 4) In case of saline used in the operation, there is significant differences in its numbers of contained microorganisms between the operative stages; pre-incision, excision, and skin suture(F=17.7500, p=.0000). 5) In case of saline exposed only to the air in the given time, there is significant differences in its numbers of contained microorganisms between the operative stages; pre -incision, excision, and skin suture (F=6.3807, p=. 00031).