This study was performed to clarify how disturbance of lipid metabolism occurred in patients with protein-losing enteropathy (PLE) as compared with that of control individuals and patients with malabsorption syndrome. Analysis of plasma lipids at fasting state showed a decreased proportion of essential fatty acid, especially linoleic and arachidonic acid fractions in patients with malabsorption syndrome as well as in patients with PLE group A, which was due to proven disorders of intestinal lymphatics. An increase in percentage of oleic acid fraction and a percentage increase in plasma triglyceride levels after an oral administration of olive oil was depressed in patients with malabsorption syndrome and PLE group A when compared with that of normal subjects. Patients with PLE group B, which was not due to major lymphatic disorders, were similar to normal in these parameters. These abnormalities were found to be marked when remarkable abnormalities of lymphatics were accompanied.