The use of multivitamin-mineral supplements has become increasingly common, but whether the use of such supplements improves micronutrient status remains still unclear. The objective of this report is to investigate how a long-term vitamin-mineral supplementation following the US Recommended Daily Intake (RDI) affected the plasma levels of selected nutrients in a subset (No. = 407) of participants in the Italian-American Clinical Trial of Nutritional Supplements and Age-related Cataract (CTNS). The CTNS was a double-blind, single centre, controlled clinical trial of 1020 participants aged 55-75 years randomized to a daily tablet of Centrum(R) or placebo. A representative sample of 40% of the 1020 subjects, whom plasma level of selected vitamins was determined at the baseline, was retested throughout the treatment period that averaged 9.0 +/- 2.4 years. Participants assigned to Centrum(R) showed a significant increase (p < 0.005) in mean/median plasma levels of vitamin E, beta-carotene, folate, and vitamin B12, and an improved riboflavin status when compared with participants assigned to placebo. Differences concerning vitamin C were statistically less relevant and those concerning vitamin A were at a borderline level. In the treated group the effect of supplementation on plasma levels of vitamins A, E, and C, and on the glutathione reductase activation coefficient was significantly higher in participants with lower nutritional status at baseline.