Infectious Bovine Rhinotracheitis (IBR) initially occurred at Kaohsiung in June, 1986, then, spread to Pingtung and Tainan, Eventually, the disease gradually disapp-eared. In 1987, the cattle were al1owed to import and resulted in an outbreak of the disease again. IBR outbroken in I 987 caused more adult cattle to be death and abortion when compared to that outbroken in 1986, It was suggested that the viruses induced the outbreak of the disease in 1987 were more virulent. Seventy-nine strains
of IBR virus were isolated during those two outbreaks.
The distribution of virus in organs of infected cattle was examined. The results showed that virus titers detected from the nasal lesions with ulcer (106 TCIDso /mJ). tonsil, placenta and tracheal mucus were higher than those from others. The most predominant ratio of virus isolation was obtained from the nasal discharges (64.3%). The agar gel precipitation (AGP) test was made on 3261 serum samples collected from eachdiary cattle. The results indicated that 716 of 3261 samples with AGP antibody to IBR virus were detectable.