For histochemical observation of vitamin D the authors contrived a new method using fluorescence microscopy. The procedures of the method were described. By this method vitamin D was found as yellow granules in the cytoplasm of the cells. Its distribution in the digestive canal, liver, lungs, spleen, adrenal glands, kidneys etc. were studied, and the authors concluded that the vitamin is mainly absorbed from the jejunum and ileum, stored in the liver adipose tissues, adrenal glands, lungs, spleen, bones, etc. and excreted chiefly from the small intestine and kidneys.