Hyperhomocysteinemia is an independent risk factor for cardiovascular morbidity and mortality in end-stage renal disease (ESRD) with an increased relative risk (RR) of 1% per micromol/L in total homocysteine concentration. In ESRD patients who undergo hemodialysis (HD), the antioxidant system is largely inadequate in correcting the imbalance between generation and scavenging of reactive oxygen species (ROS). To clarify the role of several cellulosic (CMs) and noncellulosic of synthetic membranes (NCMs) upon hyperhomocysteinemia and the oxidative stress, we measured plasma (P) homocysteine (t-HCY), plasma lipid peroxidation (LPO), and erythrocyte (E) concentration of several antioxidant enzymes in 20 normal subjects, in 35 HD patients treated with CMs, and in 29 patients treated with NCMs. Before, during, and after the first session of the week (at times 0', 120', end, 30' after HD end), blood samples were drawn. Plasma (P) homocysteine (t-HCY), cysteine (CYS), malondialdehyde (MDA), erythrocyte (E)-glutathione (GSH), glucose-6-phosphodehydrogenase (G6PD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), and superoxide-dismutase (SOD) were determined. The dialytic procedure significantly decreased the three plasma parameters, but none normalized (as a mean). The E-enzymes scavenging ROS (lower than normal before session) increased throughout the session, but the normal range of activity was never reached. Different membranes have shown different effects. When these effects on P and E spaces were pooled, we were able to classify the membranes as follows. In a general sense, cellulosic membranes are less effective than synthetic membranes both on lipoperoxides (LPO) and antioxidant activity (AOA). Among synthetic membranes, PMMA is the best membrane both for plasma values and lesser enzymatic derangement during the session. A practical system for classifying the anti-atherosclerotic action and antioxidant activity of dialytic membranes is proposed.