The fallen bacteria detected in Shimane Medical University Hospital and Shimane Central Hospital were studied on 28th November and 14th December in 1979. The mean number of the colonies of the fallen bacteria detected in Shimane Medical University Hospital was 11 and was one-fourth in the case of Shimane Central Hospital (43 colonies). In both the Hospitals, the fallen bacteria consisted of mainly Gram-positive cocci (more than 70 %) and of a remarkably low ratio of Gram-negative rod-shaped bacteria (5-8 %). It was also found that the ratio of Pseudomonas aeruginosa which frequently causes nosocomial infections was on almost negligible level (0.08%) in both the hospitals.