SummaryGastric dilatation‐volvulus (GDV) was surgiclly induced in 10 dogs. Five of the dogs were pretreated with 50 mg/kg PO of allopurinol to determine the effect of xanthine oxidase inhibition on the pathophysiology of GDV. After 150 minutes, the GDV was corrected, and lactated Ringer's solution was administered intravenoulsy (resuscitation). Two hundred forty minutes after relief fo GDV, the dogs were euthanatized without recovery from anesthesia. Administration of allopurinol was associated with a reduced (P<0.01) incidence of hepatic necrosis and a lower (P<0.045) serum phosphorus level than observed in the control group at the end of the experiment. The increase in base deficit in the allopurinol‐treated group after resuscitation was also less(P<0.045) than the control group. In conclusion, this study suggests that inhibition of xanthine oxidase‐derived oxygen free radicals protects against hepatic necrosis in dogs with GDV. Resuscitation appears to be a time of profound physiologic stress for dogs wit