Hemorrhage is one of the most prominent manifestations produced by the parenteral administration of various snake venoms especially of Habu (Mitsuhashi et al., 1959; Ohsaka et al., 1961) and other species of Crotalidae (Fidler et al., 1940; Taube et al., 1937) . In order to study the principle (s) responsible for hemorrhage caused by snake venom, a quantitative method for the determination of hemorrhagic activity is required. Up to date, however, few attempts have been made to establish the quantitative estimation of hemorrhagic activity of snake venom. Minton (1956) and Mitsuhashi et al. (1959) tried to estimate the hemorrhagic activity but the results they obtained were not reproducible in our hands.
The present authors proposed a new method, which consists of the following procedures; (1) intracutaneous injection of venom into the depilated back skin of rabbits; (2) accurate measurement of the size of hemorrhagic spot carried out from the inside of the removed skin; (3) application of the parallel line assay method for the estimation.
By this method it was possible to study the relationships of hemorrhagic activity to proteolytic and other pathological activities of Habu venom (Ohsaka et al., 1960, 1961) . In this paper, details of the new method will be presented.