Recent studies suggest that weekly administration of oral iron prevent iron deficiency as much as daily administration, while it may produce fewer side effects. These studies are based in the hypothesis that continuous administration of iron will induce mucosal block to iron absorption. A weekly dose schedule would allow renewal of the iron loaded enterocyte avoiding iron absorption blockage. To test this hypothesis iron bioavailability was studied using a double-isotopic method in two groups of 14 women, aged 31-50 years. The first group received 60mg of elemental iron, as ferrous sulfate, for 6 days and the second group 120mg every 7 days for 3 weeks. In both groups the last 240mg of iron were radioisotopic labeled. Iron absorption obtained with daily or weekly dosages were not significantly different (8.9% and 10.9%, respectively). However, this design does not shed light on the possible iron blockage. Demonstration that the absolute amount of iron absorbed is similar with both schedules, has practical implications for iron supplementation programs.