The aim of the present study was to demonstrate the possible transplacental transmission of I-131 labeled recombinant human erythropoietin (I-131-rh-EPO) in pregnant rats and its distribution through maternal and fetal organs. Six Wistar Albino Rats in their pregnancy of 18 days were used I-131 labeled recombinant human erythropoietin (specific activity = 2.4 mu Ci/IU) was injected into the tail vein of rats. After 30 minutes labeled erythropoietin infusion maternal stomach, kidney, lung, liver, brain and heart as well as fetus were removed. Then, the same organs were removed from each fetus. Measuring weight of maternal and fetal organs as well as placenta were followed by radioactivity count via Cd(Te) detector. I-131 labeled recombinant human erythropoietin was found to be able to pass rat placenta and its distribution order in fetal organs was similar to those of maternal organs. Besides, as measurements were performed closer to cornu uteri, uptakes were decreasing in every fetus and its corresponding placenta.