The selenium (Se) bioavailability of a diet consumed by a low income population in the State of São Paulo, Brazil, was assessed in Wistar rats by determining the apparent selenium absorption and retention, as well as the selenium concentration and level of glutathione peroxidase activity in plasma and liver. The study used three groups of eight selenium-depleted rats which were given the following treatments: group 1, diet prepared based on the São Paulo regional diet, with 0.02μg/g Se; group 2, a casein-based diet with 0.03μg/g Se; and group 3, a casein-based diet with 0.1μg/g Se. All diets were isoproteic. The diet based on the regional diet of São Paulo presented the smallest selenium bioavailability as assessed by the apparent absorption index, the level of selenium in plasma and liver and the glutathione peroxidase activity in plasma and hepatic cytosol. It seems that confounding factors such as deficiency in vitamins and essential amino acids, as well as the fibre fraction, might have contributed to the low selenium bioavailability recorded in this diet.