Nickelcarbonyl (Ni(CO)₄) is quite a toxic volatile substance and has a special hygienic significance within metalcarbonyls. Its recently revealed utility as a catalyser for the synthesis of acrylic esters makes it more necassary to keep it from accidental exposure. The author intended to make a few studies in Nickelcarbonyl-poisoning for preventive purpose. I a) The Nickel-Value which accrued in the organs of mice exposed to Nickelcarbontl of low concentration was almost proportional to the frequency of exposure and the value is different accordinig to kinds of organs. The amount of Ni in lung (per gram) was the largest and those in liver, kidney, heart were lower respectively and that of brain was the lowest. b) The studies of Rabbits injected with Ni (CO)₄ indicate that the decrease of Bodyweight of experimental animals treated with Ca-EDTA. and Dimercaprol (Bal) was lower compared with that of controls, and the amount of Albumin, Glucose, Urobilinogen and coproporphylin in urine was also smaller than of untreated. The change of blood of control was some-what more evident but not significant. a) The Studies on Ni-Value in organs of experimental animals injected with Ni(CO)₄ indicate that the groups treated with Ca-EDTA. and Bal gave evidently smaller amount of Nickel than those untreated. We can expect some Effect for Ni(CO)₄-poisoning by use of Ca-EDTA. and Bal. II Each mixture of Active Carbon, and Silica Gel was examined to decide the relative capacity of adsorption in to Ni(CO)₄-Vapor, and Thiocarbamide to Nickelcarbonyl. a)The results are that Active Carbon, Silica Gel and each Mixture alike adsord a certain amount of Ni(CO)₄ and at that time it differs from CO. The mechanism of adsorption of Active Carbon and Silica Gel seems to be a physico-chemical process. The amounts of adsorbed-Ni per gram of adsorbents were different and larger in proportion to the degree of thickness of layer, and the capacity of adsorption of Active Carbon was the highest, that of each Mixture was next and that of Silica Gel was the lowest. b) The study on the Gas which had been passed through the layer of Active Carbon (or Silica Gel) and Hopcalite indicates that all mice that were subjected to it entirely survived without any disturbance after 30-minutes-Exposure to the concentration of 14, 000 ppm of Nickelcarbonyl. c) The effect of Hopcalite and Thiocarbamide themselves was none to expect and its experiment proved unsatisfactory.