As altered lipid metabolism was reported in patients with chronic renal failure, it was of value to establish the effect of fat loading on the concentration of total cholesterol (Ch), total fatty acids (TFA), β-lipoproteins (β-LP), triglycerides (TG) and free fatty acids (FFA) in serum. 194 patients with various renal diseases were examined. Abnormality in lipid handling was found not on y in uremic patients, but also in renal patients with unimpaired excretory kidney function. This abnormality was especially expressed in high fasting plasma levels of β-LP and TG in compensated pyelonephritic patients and in abnormal rise of these lipid fractions after ingestion of a fat meal. Lipid handling by compensated pyelonephritic patients was pathologically changed compared with glomerulonephritic subjects which seemed to indicate that the renal medulla might be connected with the lipid metabolism.