Marrow-free trabecular bones from dog, man, monkey, and steer were obtained by use of a special marrowwashing technique. The quantities of the various trabecular bone fractions (water, organic, volatile inorganic, and nonvolatile inorganic (ash)) found in these animals were compared with those of cortical bone. The components of each of the two types of bones from the four species were found to be quantitatively similar to each other. However, the over- all density of the contical bone was higher than that of the trabecular bone. The higher density was due to a higher ash and a lower water content found in the cortical than in the trabecular bone. On the basis of the values found, graphs were prepared and the methods for the calculation of the volume and mass of the various bone fractions when given the mass and the ratio of trabecular to cortical ash were demonstrated. (auth)