Fujino and Yanahara spring waters were used. The latter, is the strongest copper spring in Japan. Iron ion in Fujino mineral water is mainly ferric and in Yanahara mineral water mainly ferrous. Yanahara spring water promotes the action of oxidoreductase in milk and liver extract. It also promotes the action of succinic dehydrase in albino rat muscle. And this promoting action of spring water is inhibited by cyanide. Fujino is less active than Yanahara and Mitsuishi proved to be almost inactive.