The relative effects of a crude aqueous extract from Phyllanthus emblica fruit and an equivalent amount of synthetic ascorbic acid (vitamin C) in reducing the clastogenic action of cesium chloride (CsCl) in vivo on mice bone marrow cells were compared. CsC1-induced chromosomal aberrations were observed in the mice 24 hours after exposure in frequencies that were directly proportional to the dose administered. Neither ascorbic acid nor the fruit extract induced chromosomal aberrations in high frequency even after treatment for seven days. On the other hand, oral administration of either ascorbic acid or Phyllanthus emblica extract for seven days prior to exposure to CsCl for 24 hours reduced the frequency of chromosomal aberrations. This protective action of orally-administered Phyllanthus extract against damage induced by CsCl is of considerable importance in view of the possible entry of Cs into edible plants from soil and subsequently into the foodchain following radioactive fallout.