The first outbreak of bovine vibriosis in the Shikoku region occurred in 1956 in the southern district of Ehime Prefecture among dairy cows which showed such a high conception rate as 92.6 per cent in 1955.Among these cows, the conception rate was decreased to 73.9 per cent in 1956 and remained in that state in the following year. In addition, abortion became prevalent among pregnant cows since the spring of 1957, bringing about a phase of “storm abortion.” This form of epizootic was really identical with that of vibriosis which broke out in an area hitherto intact (IWATA et al.). Abortion occurred in the 5th month of fetal age as its peak and was observed from the 4 th to the 7 th months in 70.6 per cent of the total cases.When vibrio agglutination tests were performed on dairy cows kept in the contaminated district, positive tests were given by about 85 per cent of the cows tested, the percentage of cows bearing, or suspected to bear, vibrio antibody being almost 20 per cent. These results were nearly the same with those obtained from the outbreaks which had ever occurred in Kyoto, Hyogo, and Fukuoka Prefectures. Eleven breeding bulls gave negative results in bacteriological examinations of semen and preputial mucus and experimental breeding with cows. These results were not always agreeable with the epizootiological presumption. It was impossible to conclude that the breeding bulls were incriminated as reservoir of infection of this disease.When the cows giving positive and doubtful vibrio agglutination tests were treated with antibiotics, such as streptomycin, penicillin, and mastol, there was a decrease in the number of cases of non-conception and abortion due to vibrio.After an epizootic of this disease since 1956, the conception rate began to rise in 1958 and no cases of abortion have been reported due to vibrio infection.