In order to verify the opinion of Ido, Momoi & Nishisaki (Okayama-Igakkai-Zasshi 43, 163, 1931; 45, 490 & 1280, 1933; 50, 2103, 1938), that the postmortem interval of a dead body is to be estimated by means of determination of the nonprotein nitrogen of the brain, lung, liver and kidney, the authors estimated the postmortem interval of 100 dead bodies giving consideration on the weather, temperature, humidity and the other circumstances etc. In 91 out of the 100 cases each estimation gave a satisfactory result. In cases where postmortem decomposition of the corpse proved an increase (in sepsis, phosphorus poisoning, burning and parathion poisoning etc.), it is required to take special considerations in regard to the amount of nonprotein nitrogen; in the cases of dead bodies found in the water somewhat satisfactory result was obtained by applying the correction of Casper and Walcher who had observed that postmortem decomposition having been occured in the water, in which case it took place with slower speed of a third or a quarter than in the air; and in the cases in which any one or more of the 4 organs were missed or abnormal the rest organs might be used for the determination.