In the previous paper it was noted that the difference of the ratio of thiamine decomposed during heating was connected with the changes of pH, although it was not necessarily regarded as a primary factor. In the present experiment, the effects of metal ions and chlorine, including copper and iron, usually coming into cooked foods from cooking vessels, were examined, since these were thought to affect seriously on the destruction of thiamine. It was found that the amount of thiamine decomposed during heating was much correlated with the amounts of these metal ions eluted and further that the decomposed products were physiologically inactive.