Plasma selenium (Se) levels of 293 subjects (160 males and 133 females) living in Desio (a small town near Milan) were determined. Analyses were performed by graphite-furnace atomic absorption spectrophotometry with Zeeman background correction. Plasma samples were not subjected to any treatment before analysis and serum samples containing a certified Se content were used as reference materials to control the quality of the analytical determinations. Plasma Se levels were found to be distributed normally with an average value of 118.8 micrograms/l and a S.D. of 27.2 (95% of the subjects lie between 64.4 and 173.2 micrograms/l). No statistically significant difference was found between males and females, and no correlation was found between plasma Se levels and age or smoking habits.