ABSTRACT. One hundred and ninety cases of rabbits, seen at animal hospitals in Saitama and Tokyo, Japan from 1998 to 2001, with BUN values greater than 27 mg/dl were analyzed regarding their underlying and/or complicating diseases and outcomes. Gastrointestinal disorder (54 cases) was the most common disease, followed by overgrowth of molar teeth and then liver disturbance. The total mortality was 48.9% within three months, and cases showing complications such as liver disturbance or bacterial infection showed highest mortality. Cases with higher BUN values showed even higher mortality, although mortality varied depending on the complications. Therefore, the prognosis of rabbit cases with high BUN values should be evaluated based on findings from blood chemistry, together with the seriousness of the underlying and/or complicating disease. KEY WORDS: BUN, mortality, rabbit.J. Vet. Med. Sci. 65(5): 625-628, 2003 BUN values are frequently examined to diagnose clinical disorders in rabbits [3,9], as well as in dogs and cats. Though high BUN levels have been reported in laboratory rabbits in experimental surveys of nephrotoxicity [1,2,6,8,14] or models of renal dysfunction [4,7,13], BUN values in companion rabbits have not been well studied. Cases of companion rabbits with high BUN values were analyzed regarding the underlying or complicating diseases and the outcomes.A total of one hundred and ninety cases of rabbits, with BUN values greater than 27 mg/dl, were examined at Saito Animal Hospital (Saitama-shi, Saitama, Japan) and Saito Rabbit Clinic (Kita-ku, Tokyo, Japan) from 1998 to 2001. Serum creatinine was also checked in all of these cases. From the results of an investigation of 111 healthy rabbits [10], BUN values greater than 27 mg/dl and serum creatinine values greater than 1.4 mg/dl were regarded as abnormal values in this study.These cases did not show any common signs, aside from anorexia. Various degrees of anorexia were observed in 181 of 190 cases (95.3%). Depression was noted in 42 cases (22.1%), diarrhea in 37 cases (19.5%), and dehydration in 30 cases (15.8%). The ages ranged from two months to eleven years of age, with a median of 3.5 years and a standard deviation of 2.4 years. One hundred and four cases (54.7%) were males and 86 cases (45.3%) were females. Blood samples were taken from the cephalic vein, intermedial branch of the caudal auricular artery, external saphena, or external thoracic vein. In several cases, blood samples were taken from more than one site, and the site of blood collection was confirmed not to influence BUN values. BUN levels were analyzed by VetScan (Daiichi Pure Chemicals Co., Ltd.) or VetTest (IDEXX Laboratories, KK).Each rabbit was managed according to its specific condition by removing inducing factors, treating complications, and improving renal function. Fluid therapy was administered, mainly intravenously and sometimes subcutaneously, in 175 cases, and force-feeding was carried out in 71 cases. Antibiotics and/or other medications were administered in 188 case...