Virus inactivated by formalin or beta-propiolactone was superior to that inactivated by ether and heating in immunogenicity to mice. There were no significant differences in the antibody response of mice among such adjuvants as aluminum phosphate gel, aluminum hydroxide gel, and sodium arginate gel. When cattle were immunized with vaccine inactivated by formalin and adsorbed to aluminum phosphate gel, an excellent effect was obtained by injection with two doses of 3 ml each given at a 4-week interval. It was also suggested that mice and guinea pigs might be available for the potency test of vaccine. When calves and pregnant goats were injected with vaccine in the same manner as mentioned above, they were prevented from viremia and fetal infection caused by challenge virus. Even when stored at 4 degrees C for 12 months, vaccine was found to retain its stabilized immunogenicity. When pregnant cows were injected with vaccine in the field, the positive rate of neutralizing antibody was 88.5% in the 2 months after the first injection. When other pregnant cows were injected twice with vaccine, this rate was 34.6, 100, 65.4, and 45.8% in the 1, 2, 6, and 10 months, respectively, after the first injection. In another experiment, the antibody levels attained declined rather rapidly in several months. A single dose of vaccine given one year later provoked a rapid antibody response. The vaccination caused no clinical symptoms, abnormal birth, or decrease in milk yield in these cows.