An attempt to prevent epidemics of hemorrhagic pneumonia in mink due to Pseudomonas aeruginosa was made in the course of epidemics with injection of the multicomponent vaccine consisting of common protective antigen (OEP) of P. aeruginosa mixed with toxoids of protease and elastase of the bacillus. Enzootics of hemorrhagic pneumonia, due to P. aeruginosa serotype 8, broke out from August to October 1977 in a total of 13 sheds of 3 farms (A, B and C) which were located in the northeast area of Hokkaido. These farms were raising 7,452, 2,553 and 10,639 mink respectively. The mortality rate of the mink on farms A, B and C were 11.8%, 13.0% and 1.0% respectively. The vaccination was performed on the 3 farms 5, 8 and 21 days after the onset of the disease. Inoculation of each mink with 200 micrograms or 100 micrograms of each of the three components of the multicomponent vaccine was effective in most of the male and female groups of mink. The period required for revealing the effect of the vaccination was very short, in some cases only a few days. Administration of the vaccine 21 days after the onset of the enzootic was also effective.