This review describes effects of miso with reference to prevention of radiation injury, cancer and hypertension with a twin focus on epidemiological and experimental evidence. Miso with a longer fermentation time increased crypt survival against radiation injury in mice. When evaluating different types of miso provided by different areas in Japan, miso fermented for a longer period increased the number of surviving crypts, and 180 days of fermentation was the most significant. Dietary administration of 180-day fermented miso inhibits the development of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and rat colon cancers in F344 rats. Miso was also effective in suppression of lung tumors, breast tumors in rats and liver tumors in mice. The incidence of gastric tumors of groups of rats given NaCl was higher than those of the groups given miso fermented for longer periods. Moreover, the systolic blood pressure of the Dahl male rat on 2.3% NaCl was significantly increased but that of the SD rat was not. However, the blood pressures of the rats on a diet of miso or commercial control diet (MF) did not increase. Even though miso contains 2.3% NaCl, their blood pressures were as stable as those of rats fed commercial diet containing 0.3% salt. So we considered that sodium in miso might behave differently compared with NaCl alone. These biological effects might be caused by longer fermentation periods.(DOI: 10.1293/tox. 26.91; J Toxicol Pathol 2013; 26: 91–103)