No. Ⅱ fluorocarbon blood substitute in divided doses was infused into the rats in a 12-day-period. Pathomorphological changes of the various organs of the animals were observed dynamically in the first year after the completion of the infusion. Fluorocarbon particles mainly accumulated in the organs with abundant reticulo-endothelial tissue particularly the liver and spleen. The changes of the weight of the liver and spleen and the existence of foam cells could be considered as the criteria to indicate the severity of the accumulation. It was found that at the end of the first year after the completion of No. Ⅱ fluorocarbon blood substhue infusion, the liver and spleen essentially resumed their normal weight but a small number of foam cells still existed, However, accumulated fluorocarbon particles exerted no harmful effects on the functions and structures of the organs observed.