On polyacrylamide gel (PAG) disc electrophoresis of serum lipoproteins, the band(s) which migrates between preβ- and β-lipoproteins was more frequently observed in hyperlipidemics with diabetes mellitus (73%), than in those without diabetes mellitus (37%) (P<0.01). Those bands were seen at three positions between preβ- and β-lipoproteins. A higher incidence of coronary artery disease (CAD) was observed in patients with midband as a shoulder of β-lipoproteins (44%), than in those without midband (11%) (P<0.05) after the matching of other risk factors. These results suggest that midband as a shoulder of β-lipoproteins may be a risk factor for CAD in diabetes mellitus with hyperlipidemia.