Computerized axial tomography permits accurate cross-sectional radiographic visualization of visceral organs. Thus, “radiographic area” of an organ slice can be calculated and converted to actual area from a standard grid printed on the roentgenogram. Because the width between slices is known, the volume of an organ slice can be calculated as area times width. Mass of the organ slice is then the product of slice volume and organ density, and entire mass of the organ is the sum of the masses of all the organ slices. The validity of this method was examined in four water-filled balloons, in 12 excised human cadaver organs (six kidneys, three livers, and three spleens), and in two human cadavers while the organs (four kidneys, one liver, and two spleens) remained in situ. Radiographic volume and mass agreed with actual volume and mass within ±3% to 5%, thus confirming the accuracy of this method.