For the purpose of inducing benzene poisoning in the rabbits by inhalation of benzene, the author deviced a new type of generator and inspirator of benzene gas to be maintained at a constant concentration and performed experiments of benzene inhalation with rabbits and guinea-pigs; and obtained the following results: 1. In the benzene inhalation with the rabbits, at the concentration of 15,000 p.p.m. or more, test rabbits died within several hours, and at the concentration of 10.000 p.p.m., they died within 3 weeks, and at 5.000 p.p.m. in a month. However at the concentration of 2,000 p.p.m. they all survived. 2. In the case of the guinea-pigs benzene inhalated was exhalated again almost completely within 5 hours after cessation of the inhalation. Hematological changes: 1. In general, at all concentrations, the red cell count, leucocyte count and hemoglobin content temporarily increased immediately after inhalation, but thereafter they decreased by degrees in the course of repeated inhalation. As for the leucocyte series, pseudo-eosinophil leucocyte had obviously sustaind effect on both relative percentage and absolute counts, and also the leftward nuclear shift was observed. 2. The reticulocyte count also by inhalation brought about an obvious increase temporarily, but on the other hand, it tended to increase in the last stage. 3. On the smear preparation, staining of proper granules of pseudo-eosinophil leucocytes grew poor by degrees, and when benzene was inhaled at the concentration of 5,000 p.p.m. or more, there appeared toxic granules, and violent anisocytosis and poikilocytosis was observed in the last stage.