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ABSTRACT. The hemagglutinating activity and serological properties of three strains of rabbit hemorrhagic disease virus, Chinese, Korean and Shizuoka, which was first isolated in Japan, were examined by hemagglutination (HA) and cross hemagglutination inhibition (HI) test with human erythrocytes. Similar results were observed between the Chinese and Korean strains, both of which gave positive HA at 4°C with O, A, B and AB, and at 22°C with B and AB blood groups. In the Shizuoka strain, positive HA was observed at 4°C with O, A, B and AB, at 22°C with A, B And AB, and at 37°C with B blood group. In experimentally infected rabbits, HI antibody in these animals showed a titer of 16,384 or 32,768 at 4 weeks after inoculation. No serological difference was observed in three strain s by cross HI test. KEY WORDS: antigenicity, hemagglutination, RHD virus.J. Vet. Med. Sci. 65(1): 95-97, 2003 Rabbit hemorrhagic disease (RHD) was first recorded in China in 1984 [6]. The causative RHD virus is a member of the genus Calicivirus, and has hemagglutinating activity for human red cells [7,8]. In the early stage when this disease first appeared, many investigators reported that the RHD virus has a great ability to agglutinate human O type erythrocytes [6,9,13]. Although the hemagglutination (HA) test carried out with human O erythrocytes is usually employed for viral detection in the tissue homogenates from suspected rabbits, there are reports that the RHD virus has the ability to agglutinate human erythrocytes of groups A, B and AB as well as those of group O [10,12]. On the other hand, there are some strains of RHD virus that did not hemagglutinate in general conditions at room temperature [1,2,4]. These observations suggested that the hemagglutinating characteristics of the RHD virus are not so simple, and encouraged us to investigate the hemagglutinating activity and antigenicity of the RHD virus, including the first isolate in Japan. This study presents our observations on HA with the RHD virus among human blood groups O, A, B and AB and hemagglutination inhibition (HI) by anti-RHD virus sera.Three strains, the Chinese, Korean and Shizuoka, of RHD virus were used in this study. The Chinese and Korean strains were supplied by Dr. C. Itakura, Hokkaido University, Sapporo, Japan. The Shizuoka strain was first isolated in Japan from the liver of naturally infected rabbit in 1995 [3]. Although young rabbits did not show any clinical signs, fifty-three of 60 (88.3%) adult rabbits, aged three months or older, died within a period of 9 days of this outbreak. The infected rabbits suddenly showed depression and convulsion, then died within several hours. Some of them cried out just before death.Three kinds of HA antigen were prepared from livers of adult New Zealand white rabbits which had been injected intramuscularly with 1 ml of each viral strain, respectively. A 20% W/V liver suspension was prepared in phosphate buffered saline (PBS) (pH 7.2). After centrifugation (10,000 × g for 60 min at 4°C), the supernatant was filtered wi...