Summary Ascending cholangitis was induced in dogs by performing a biliodigestive Roux-Y anastomosis. Then two valvular antireflux mechanisms were performed on separate groups of these dogs with the aim of preventing the onset of ascending cholangitis. One was performed by a laterolateral plicature at the intestinal anastomosis and the other by invagination of the mucosa in the nonworking loop that had been anastomosed to the bile duct. All the dogs underwent analytic tests over a period of 3 months and histopathologic tests at the end of the study period. Results showed cholangitis and pericholangitis in the liver biopsy specimens of the group with no antireflux valve, to a lesser degree in the group with laterolateral plicature, and almost none in the animals with the invaginated valve.