HLA (A and B) antigens, blood group systems (ABO, Rh, MNSs, P, Kell, Lewis and Duffy) and serum group systems (Hp, Tf, Pi, C3 and C4) were studied in patients with intermittent claudication (IC) and controls. HLA antigen A 28 was significantly more common, and blood group 0 was significantly less common among the patients than among the controls. A comparison between patients with IC and those with abdominal aortic aneurysms showed a significant difference between these two groups concerning the MN blood groups.