Objective: The present study was designed to examine for the first time, side-by-side, the effects of plant sterol and stanol consumption on lipid metabolism and markers of antioxidant status, oxidative stress, endothelial dysfunction and low-grade inflammation in subjects on stable statin-treatment. Design: Double-blind, randomized, placebo-controlled, intervention trial. Setting: University. Subjects: Forty-five patients on current statin treatment were recruited via newspaper advertisements. Data of 41 patients were used in statistical analysis. Intervention: Subjects consumed margarine with no added plant sterols or stanols for 4 weeks and were then divided into three groups of 15 subjects. For the next 16 weeks, one group continued with the control margarine and the other two groups with either a plant sterol-or stanol (2.5 g/day)-enriched margarine. Blood was sampled at the end of the run-in and intervention periods. Results: Plant sterol and stanol consumption significantly (P ¼ 0.026) reduced low-density lipoprotein (LDL) cholesterol by 0.34 mmol/l (95% confidence interval (CI), À0.67 to À0.04 mmol/l). No effects were shown on enzymatic and non-enzymatic antioxidants and markers of oxidative modification of lipids and DNA. In addition, no effect was found on soluble adhesion molecules, C-reactive protein and monocyte chemotactic protein-1 concentrations. Conclusions: We conclude that 16 weeks of plant sterol or stanol consumption did not affect markers of antioxidant status, oxidative stress, endothelial dysfunction and low-grade inflammation in patients on stable statin treatment, despite a significant reduction of LDL cholesterol.