The results of plasma lipid and lipoprotein analysis in two related patients, brother (R.U.) and sister (R.R.) with analbuminemia, and three first-degree relatives (parents and sister) are reported. Both patients showed a remarkable increase in cholesterol and phospholipid levels, and there was a corresponding increase in serum apo B and apo A-I. This hyperlipidemia is due to a selective increase in LDL and HDL concentrations. R.U. showed an increase in both HDL2- and HDL3-cholesterol, R.R. only in HDL3-cholesterol. VLDL concentration was reduced in R.U. and normal in R.R. The plasma lipoprotein electrophoretic pattern did not correspond to any of the phenotypes in Fredrickson's classification. Composition of the different lipoprotein fractions was normal in the patients and family members. Serum FFA level in R.R. was very low. An increase in the plasma protein fractions, particularly the transport fractions, was confirmed in both patients. The possible pathophysiology of the hypercholesterolemia in these patients is discussed. Unlike other reported cases, clinical signs of atherosclerotic complications were absent.