Brazil nuts (Bertholletia excelsa) natively contain very high concentrations of selenium. Since dietary selenium, including Brazil nuts, have been associated with protection against tumor development in laboratory animal studies, it was of interest to determine the selenium content of the nuts from different nut-growing regions of Brazil. In the work reported, 162 nuts from each of two regions (Acre-Rondonia and Manaus-Belem) were individually analyzed for selenium. The average +/- standard deviation and range of selenium concentrations in ppm, fresh weight for nuts from Acre-Rondonia and Manaus-Belem regions were, respectively, 3.06 +/- 4.01 (0.03-31.7) and 36.0 +/- 50.0 (1.25-512.0). The toxicology of Brazil nut consumption is discussed.