In the age when there are so many users of narcotic drugs as at the present, it is rather surprising that nothing definite is known about the concentration of barbital in blood after its administration; and this can be keenly realized if one takes into consideration the fact that barbital is one of the most frequently used narcotic drugs. This aroused my interest in intiating the study on the barbital concentration in body. I have examined human body repeatedly with the use of Goldschmidt's method and measured the barbital concentration in blood. As the results, it has been found that the barbital concentration in blood reaches its maximum about two hours after its administration, and although it gradually decreases thereafter, it still maintains a relatively high level after twenty-four hours. This point coincides well with that of drugs clinically used for inducing lasting sleep.