Diets containing spores of B. moritai were fed to mice for 7 months. For the comparative microbe, B. thuringiensis was adopted. Bacterial detections were conducted on tissues as well as blood at the 3rd month, the 7th month of feeding and two weeks following termination of the diet. The following results were obtained.1) Detection of bacteria in blood was confined to a few cases and consistency was unrelated to diet concentration. On the contrary, a considerable amount was detected in the spleen, kidney, lung, liver and heart, and was dose-related. The bacteria showed, however, no pathogenic activities during the course of the experiment.2) Despite continuation of the diet, a lower accumulation was found at the 7th month than at the 3rd. After withdrawal from the test diet, a rapid decline of bacteria or total disappearance was observed.3) The pattern of accumulation of B. moritai in tissues was similar to that of B. thuringiensis with no apparent differences in general toxicological features.