This twenty-fifth quarterly report of the research and development activities of the Radiological Sciences Department, Hanford Atomic Products operation, as before, includes some items charged to control but included for general interest. The previous report of this series was numbered: HW-39624, October 11, 1955. Progress is reported in the following studies: a radiobiological-ecological survey of the Columbia River; the toxic effects of continuous low-level exposure to I¹³¹ in pigs; Pu metabolism in miniature pigs and rats; the tissue distribution and retention of Ru¹⁰⁶ and Cs in rats and mice; the radiosensitivity of the intestine of rats; the pulmonary absorption of radioactive particles and the pathological effects of such particles in the lungs of mice; the uptake of I¹³¹ and other fission products from the soil and from air by plants; determinations of the relative biological effectiveness for yeast cells of Po²¹⁰ alpha particles and P³² beta particles; the development of chemical and radiological monitoring methods; the separation of fission products from waste streams; and improvements in instruments for monitoring and low-level radiation counting. The status of the research programs of the department is reviewed.