The hematopoietic cells of tadpoles occur in the caudal portion of the kidneys and undergo extensive mitotic division. They are destroyed by hard X-rays with a dosage of 500 r, leaving very few remaining after the lapse of 7 days. 196 tadpoles of Rana catesbiana were used in these expts. A study of cell destruction in tadpoles refrigerated at 0[degree] to 5.5[degree]C showed that these low temps. preserve all but a very small percent during the 24 hrs. of refrigeration. The ratio of destruction in the refrigerated compared with that at normal temps. (averaging 18.9[degree]C) ranged from 1:6 to 1:33. In one series of 58, tadpoles refrigerated for 4 days showed extremely little cell destruction, while those removed at the end of 2 days and maintained for 1 day or 2 days at normal temp. showed a very great amt. of destruction. Refrigeration before and during X-ray treatment did not give results appreciably different from those produced by refrigeration after irradiation. Thus, refrigeration prevents the degeneration of X-rayed hematopoietic cells but does not prevent the primary injury that leads to their degeneration at normal temps.