The orange and red plant pigments beta-carotene and lycopene score high as antioxidants in the test tube. But their antioxidant capacity seemed to disappear in human blood. However, a new assay that peers into blood lipids shows that these antioxidant nutrients have been doing their job in our blood all along. Beta-carotene, lycopene and other fat-soluble antioxidants hang out in the lipid portion of human plasma. But popular assays measure antioxidant capacity of the water portion only, where vitamin C and other water-soluble antioxidants settle. Oxidation events generally begin there, but the chain reactions they set off readily cross over into the lipid portion of plasma and vice versa. According to Kyung-Jin Yeum, nutritionist at the Jean Mayer US Department of Agriculture (USDA) Human Nutrition Research Centre on Aging at Tufts University (funded by the USDA's Agricultural Research Service), the new assay, which measures oxidation in both environments, gives a truer picture of total antioxidant capacity of biological samples. Ultimately, the assay will help health professionals better recommend the antioxidants an individual needs to boost protection against heart disease, cancer and other age-related diseases. These are believed to evolve, in large part, from cumulative oxidative damage to cell components. Giancarlo Aldini, a chemist at the University of Milan in Italy, developed and validated the assay with Yeum and her colleagues at the Boston centre. The researchers named the assay SOLAC for selective oxidisability of lipid and aqueous compartments. By early next year, they plan to have the lipidand aqueous parts of the assay, both done in a fluorescence detector, combined into a single run and automated to handle about 100 samples at a time. They are gearing up to assay plasma samples from two large-scale population studies to look for correlations between true antioxidant capacity and heart disease or eye disease. If they find correlations, results from SOLAC could serve as a biomarker for risk of these diseases.