1. The formation of siderocyte was not observed on the subcutaneous injection of nitrobenzol into healthy canine. 2. No remarkable influence of siderocyte was not shown on the intravenous injection of l-ascorbic acid, isotonic hemoglobin solution, hypotonic hemoglobin solution and aseptic distilled water. 3. The formation of siderocyte was promoted of the subcutaneous injection of phenylhydrazine into healthy canine. 4. Siderocyte was increased on the cases with thrombosis of the reticuloendothelial system or poisoning of carbon tetrachloride. The increae of siderocyte was appeared in a little delay and the measure was high on that cases. It was thought that siderocyte was mainly disposed in the reticuloendothelial system. 5. Observing, on the forming condition of siderocyte after standing the withdrawn blood in various grades, the formation of siderocyte was already promoted at the time thought occuring the mobilization of deposit blood and it was timely and quantitatively promoted after 24 hours of blood extraction at which time the mixture of the incomplete newbone erythrocyte made rapidly. 6. It was thought that the formation of siderocyte and increase of pseudohemoglobin in erythrocyte were the same genesis.