Total and lipid-bound sialic acids in the blood were measured and lipoprotein metabolism assessed in 219 men and women with primary (n = 129, coronary patients) and secondary (n = 66, patients with type II diabetes) hyperlipoproteinemias and normolipidemia (n = 24, normal subjects). The level of total sialic acids in coronary patients reliably differed from that in normal subjects or diabetics. The level of lipid-bound sialic acids was the same in coronary patients and normal subjects and reliably higher in diabetics. The results do not confirm the hypothesis about the probable diagnostic value of total and lipid-bound sialic acids as markers of coronary disease and coronary atherosclerosis. Measurement of total sialic acids may be one of the tests verifying the disorders of lipoprotein metabolism.