O-Nicotinylthiamine disulfide was administered to patients with impaired pulmonary function in a dosis of 125mg per day (equivalent of B_1・HCl) for 4 weeks. There was no change in red blood count, white blood count, zinc sulfate test, total cholesterol, serum-GOT and serum-GPT, slight decrease in hemoglobulin and serum protein, and mere increase in albumin globulin ratio, alkaline phosphatase and LDH.