Exchangeable pools of Se after an intravenous injection of 74Se-enriched isotope as sodium selenite were measured in two groups (n 9) of elderly women (free-living aged 64–82 years and institutionalized aged 68–82 years), and a comparison group (n 9) of young women aged 31–40 years to evaluate the effect of age and institutionalization on Se reserves. Dietary Se intake was not different among the three groups. Plasma Se and glutathione peroxidase (EC 22.214.171.124) levels were significantly lower in the institutionalized elderly women (P < 0.05). In each of the three groups, two pools were determined from our model. The size of the first pool and the sum of the two pools were lower in the group of institutionalized elderly women than in the other two groups. The significant correlation between plasma Se level and total Se pool size (r 0.66, P < 0.01) indicated that this last variable could serve as a new marker of Se status. Finally, these data suggest that the Se status of elderly women is more related to lifestyle, in terms of institutionalization or not, than to age per se.