In order to clarify the differences in lipid metabolism between malignant neoplastic and benign cases, livers of patients were biopsied under peritoneoscopy. One half of each sample was subjected to histologic examination and the other half to lipid analyses by means of thin layer chromatography and gas liquid chromatography. Histologic examination was necessary to confirm whether the lipid metabolism in the liver of patients would be influenced by hepatic disease or not. The most significant differences between malignant and benign cases were observed when the ratio of fatty acid content of the phospholipid fraction to that of triglyceride was calculated for each patient. These ratios were over 2.20 in 40 cases out of 47 malignant neoplastic cases without benign hepatic diseases and in 3 out of 4 malignant neoplastic cases combined with benign hepatic diseases, but were under 2.19 in 35 benign cases. Moreover, 4 cases of early gastric cancer and a case of relatively early pancreatic cancer included in the malignant cases mentioned above also showed the ratios over 3.00. This finding would be applicable for the clinical diagnosis of the malignant neoplastic diseases.