ABSTRACT. A 4-year-old neutered male Chihuahua was presented with a history of anorexia and vomiting. Continuous elevation of liver enzymes was found on repeated blood examinations and the dog was referred to us for further evaluation. The absence of gallbladder was suspected on ultrasonography. Exploratory laparotomy and retrograde cholangiography confirmed gallbladder agenesis and a possible hypoplasia of the right medial and lateral liver lobes. Histologically, proliferation of bile ductules associated with portal fibrosis and pseudolobular formation were apparent in the liver lobes.KEY WORDS: cholangiography, canine, gallbladder agenesis, liver, ultrasonography.J. Vet. Med. Sci. 72(7): 959-962, 2010 Gallbladder agenesis (GBA) is an extremely rare condition in dogs and there have been only two reports in young female Maltese dogs [2,15]. It is also a rare condition in humans, reported in both newborns and adults, with a reported incidence between 0.01% and 0.075% [3,18,19]. In human adults, most cases are found incidentally during either abdominal surgery or autopsy. In newborns, it is often associated with other life incompatible anomalies [5,6,10]. Two of the reported dogs with GBA were relatively young when diagnosed (11-month-old and 7-month-old) [2,15]. The etiology of GBA is unknown both in dogs and humans, but in humans it is generally thought to be a developmental failure of the pars cystic from which the gallbladder arises during embryogenesis. It is also suggested in humans that there are familial hereditary forms of GBA [21,24]. In this report, we present a Chihauhau with progressive hepatopathy possibly due to GBA which was suspected based on ultrasonographic findings and subsequently confirmed by exploratory laparotomy and retrograde cholangiography.A 4-year-old, 3.5 kg, castrated male Chihuahua was examined by the referring veterinarian for a 3-day history of anorexia and vomiting. Blood examination revealed increased alanine transferase (ALT, 372 IU/l) and alkaline phosphatase (ALP, 1,020 IU/l). The results of complete blood count were unremarkable. Amoxycillin, ursodeoxycholic acid, S-adenosylmethionine, and glutathione were prescribed. At follow-up evaluations, the owner claimed that the clinical signs had resolved; however, the liver enzymes continued to elevate (at 3 months after the first admission; ALT >1,000 IU/l, AST 318 IU/l, ALP 1,020 IU/l).The dog was referred to the Veterinary Teaching Hospital of Iwate University three months after the clinical onset. On presentation, the dog was alert and the physical examinations revealed no abnormalities. The results of complete blood count were within normal limits. Serum biochemistry panels revealed marked elevations of liver enzymes; ALT 961 IU/l (reference range 11-69 IU/l), AST 500 IU/l (reference range 7-49 IU/l), ALP 1,022 IU/l (reference range 14-193 IU/l), and gamma-glutamyl transpeptidases (GGT) 26 IU/l (reference range <9.0 IU/l). Fasting and postprandial ammonia levels were 18.0 and 40.2 g/dl, respectively (reference range 15-88 ...