Some bibliographic data suggest that serum lipids bound to monotypic immunoglobulins (Ig-s)could represent one specific type of dislipidaemia in man. In this paper 5 cases confirming such a suggestion are described. After agarose gel electrophoresis lipids bound to monotypic Ig-s moved as one separate lipoprotein category clearly different from alpha and beta lipoproteins. The electrophoretic mobility of Ig-s binding lipids was not always the same and depended on the immunochemical isotype of Ig (fig. 2). The lipid concentration in the sera, containing lipid bound Ig-s was found to be very low (table 1). Both neutral lipids and phospholipids were extracted from the isolated monotypic Ig-s (figs 4 and 5, table 2).