The lipid and fatty acid metabolism of tissues and plasma of rats was studied one week and three months after insulin deficiency was induced in the rats by treatment with strept-ozotocin. The fatty acid content was analyzed by microcapillary column gas-liquid chromatography. In the liver, significant decreases in triglyceride, cholesterol and phospholipids were observed after one week, and significant decreases in triglyceride were observed after three months. No changes were observed in the heart. In the lung, remarkable decreases in triglyceride and phospholipids were observed after three months. Significant decreases in arachidonic acid were observed in the liver, heart and lung. Significant decreases in palmitic acid were observed in the lung and adipose tissue.