Plasma levels of nutrients in 196 individuals were assayed as part of a study of the feasibility of a nutrition intervention trial in Linxian, a county in North Central China with exceptionally high rates of esophageal cancer. High-performance liquid chromatography analyses of samples collected in April 1983 showed low (relative to United States standards) base-line levels for retinol, alpha-tocopherol, and beta- and alpha-carotene. Repeat sampling in August 1983 revealed significantly increased plasma levels of retinol and alpha-tocopherol among those who had in the interim received daily supplementation with multivitamin pills containing the Recommended Dietary Allowance levels of those nutrients but not among those without supplementation. Levels of carotenes, which were not included in the pills, tended to increase regardless of supplementation, consistent with seasonal variations in availability of carotenoid-containing foods. Atomic absorption spectrophotometry analyses showed essentially normal levels of copper and zinc in plasma. Neither was affected by vitamin supplementation (the pills did not contain minerals) nor seasonal variation. The data are generally consistent with prior biochemical surveys in indicating marginal or low status of several nutrients in Linxian and in showing that supplementation with vitamins can effectively raise blood nutrient levels.