High density lipoprotein (HDL) fractions were separated by dextran sulfate-Mg++ from sera of 5 healthy males before and after oral administration of a daily 1200 mg dose of Nicomol (2,2,6,6-tetrakis (nicotinoyloxymethyl) cyclohexanol; Cholexamin, Kyorin Pharmaceutical Co. Ltd.) for 2 weeks. The HDL fractions were further subdivided into HDL2e and HDL3e by Utermann's electrophoretic method on polyacrylamide gel containing lauric acid. These subfractions roughly corresponded to HDL2 and HDL3, respectively, which were separated by ultracentrifugation. Nicomol treatment increased the HDL2e/HDL3e ratio as is observed for the HDL2/HDL3 ratio, in addition to the increase in total HDL cholesterol concentration. The electrophoretic determination of HDL2e/HDL3e ratio in combination with HDL cholesterol level seemed to be clinically important in assessment of the alteration of HDL2 and HDL3 under physiological and pathological conditions.