The experimental caustic effects on the rabbit's esophagus are produced with 3.0 cc of 12.0% acetic solution. The macroscopic and histopathological findings of esophagus and stomach in acute early stages have been carefully followed. The findings in the esophagus and stomach begin from the first day after the ingestion of acetic acid. These changes are characterized by congestion and dilatation of blood vesseles of the mucosal and muscle layer accompained by necrobyosis, necrosis and karyolysis. The changes become progressively severe and reach its maximum at te end of the 5th day. The regenerative activity including fibrous proliferation begin from the 7th day. The findings in the liver and spleen begin from the first day after the ingestion of acetic acid. These changes are characterized congestion and dilatation of blood vesseles and destruction of parenchyme tissue cell. The possibility of direct inflowing of the caustic solution into the blood streem cannot be excluded. However, the cause of tissue change of liver and spleen has been considered as the absorption of substances from tissue destruction in the esophagus, stomach and intestine.