Human erythrocytes were used in vitro to investigate the effect of the hepatocarcinogen N-nitrosodiethylamine (NDEA) on lipid peroxidation (LPO) and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR). LPO and erythrocyte haemolysis increased with increasing concentrations of NDEA and with increased exposure time. CAT activity decreased while GR activity increased with both the increasing concentrations of NDEA treatment and exposure time. However, no alteration was observed in SOD enzyme activity. The inhibitory effects of antioxidants and free radical scavengers such as EDTA, succinic acid, sodium benzoate and ascorbic acid were observed. These agents lowered NDEA-induced LPO and haemolysis in erythrocytes. This might indicate that the generation of free radicals and subsequent LPO may play a role, at least in part, in inducing NDEA toxicity.