A survey of the incidence of Salmonella in samples collected from three treatment plants of sewage, food-poisoning, sporadic case with acute enteritis and healthy carrier in a local city, was performed from Aprile 1974 to December 1978. Salmonella were very frequently found in Influent sewage. The range of sewage source serovars found was wide and most aerovara were related with human source. A total of 954 strains and 62 serovars of Salmonella were found in sewage and human source. S. typhimurium, S.tennessee, S.thompson, S.infantis, S. senftenberg and S.oranienberg were the most frequent aerovars. It might be presumed that the environmental contamination of the area by the organisms is increasing gradually, since new aerovars of Salmonella, for example S.havana, S.agona, S.london, S. mission and S.cerro etc., which were never found in Nagano prefecture before, were isolated in the area. Effect of addition of the Aluminum sulfate and Polyacrylamide for Salmonella isolation from sewage, were studied. By use of the floe method. Salmonella were more frequently isolated from influent sewage.