The experiment was performed on 115 Wistar rats divided into 3 groups: I – the controls, which were administered i.g. with 14 kBq per rat with Cs-137 and the radioactivities of internal organs and muscles 16 samples were measured on days 1, 3 and 7; II – treated with ferric ferrocyanide FF or ammonium-ferric-cyano-ferrate AFCF on day 1 after the Cs-137 administration and thereafter they followed the same procedure as the controls; III – treated with FF or AFCF 2-fold/day for 5 days and the organ radioactivities were measured on day 7. The results indicated that FF and AFCF increased the biological elimination of Cs-137, especially on days 1–3. The decontamination effectiveness of AFCF was higher than that of FF. The repeated treatment increased the decontamination effectiveness.