The major plasma lipoproteins of the adult sheep were high density lipoprotein (76%) having α‐mobility on electrophoresis and low density lipoprotein (20%) having β‐mobility. Chylomicrons and very low density lipoproteins were minor constituents (<5%). The postabsorptive hyperlipidaemia in suckling lambs is mainly a result of increased concentration of low density and high density lipoproteins although the relative contribution of very low density lipoproteins was increased to 7—15% of the total lipoproteins. The hyperlipidaemia was markedly greater in an intact male lamb than in female or castrated male lambs. In suckling lambs a new lipoprotein (density 1·090 g/ml) appeared in the high density lipoprotein fraction but disappeared before weaning.