Oxidative stress may play a role in the pathophysiology of diabetes and cardiovascular disease, but little is known about antioxidant status among individuals with the metabolic syndrome who are at high risk for developing these conditions. Using data from the Third National Health and Nutrition Examination Survey (1988-1994), we compared circulating concentrations of vitamins A, C, and E; retinyl esters; five carotenoids; and selenium in 8,808 U.S. adults aged > or = 20 years with and without the metabolic syndrome. After adjusting for age, sex, race or ethnicity, education, smoking status, cotinine concentration, physical activity, fruit and vegetable intake, and vitamin or mineral use, participants with the metabolic syndrome had significantly lower concentrations of retinyl esters, vitamin C, and carotenoids, except lycopene. With additional adjustment for serum lipid concentrations, vitamin E concentrations were significantly lower in participants with the metabolic syndrome than those without the syndrome. Retinol concentrations were similar between the two groups. After excluding participants with diabetes, the results were very similar. Consumption of fruits and vegetables was also lower among people with the metabolic syndrome. Adults with the metabolic syndrome have suboptimal concentrations of several antioxidants, which may partially explain their increased risk for diabetes and cardiovascular disease.