Aim To study possible clinical relationships of myeloperoxidase(MPO) and carotid atherosclerosis in non-diabetic patients with maintenance hemodialysis(MHD).Methods Levels of plasma MPO and serum elastase(ELT) of non-diabetic patients with MHD were determined by ELISA.Carotid intima-media thickness(IMT),quantity and area of carotid plaque were measured by B-mode ultrasonography.Results There was no significant difference of serum ELT before and after hemodialysis(HD).Plasma MPO was significantly higher after HD than before HD(P<0.01).There was positive correlation between age,MPO level before HD and carotid IMT(P<0.01).There was no correlation between the levels of plasma MPO after HD and serum ELT or carotid IMT.Conclusions MPO level before HD contributed to carotid atherosclerosis in patients on MHD.In contrast,there was no relation between higher MPO level after HD and carotid atherosclerosis.This finding suggests that increased plasma MPO levels after HD do not reflect increased activation/degranulation of leukocytes and supports the view that the increase in circulating MPO reflects the heparin-induced release from the atherosclerotic vascular wall.