In view of the fact that the determination of body fat has very important bearing on the selection of certain naval and aviation personnel who may be subjected to sudden changes in environmental pressures, on veterinary economics, clinical medicine, nutrition, gymnastics as well as metabolic studies 43 males were chosen for a preliminary survey of their body fat content. Two relatively simple indirect methods for determining body fat were employed, namely: Behnke's specific gravity method and McCance's density-SCN combined method. In obtaining the sp. gr. of the body in each case the method was, however, modified in two respects. Firstly, due attention was paid to the temperature of the water in which the subject was immersed, and secondly, the amount of gas was ascertained in the lungs of the immersed subjects by asking them to expire into the spirometer while still in water instead of after getting out of the water as practiced in McCance's procedure.The average fat content of the 43 males in terms of body weight when calculated according to the method of Behnke's formula and modified method was 14.4% and 13.2% respectively. Analysis of the results showed that the body fat content obtained by Behnke's method was higher than that obtained by the modified method, the only exception being that case when the temperature of the water was at 37℃. It was also found that the lower the temperature of the water, the greater was the difference between the two methods. It is therefore important to keep the temperature of the water constant (preferably at body temperature) or to record the temperature, if not constant, and give due consideration to it in making the calculations.McCance's combined method was used on only 38 subjects out of the 43 and was carried out in two series. The average body fat content of the subjects in the first series was 12.7%, a figure significantly smaller than either one of Behnke's or the modified method in the same series. In the second series the fat content was 11.2%, with no statistical difference between it and either one of the above two. Therefore, in our opinion, this combined method needs more careful evaluation before being put into general use.