This study was undertaken to evaluate a central cooling technique for heatstroke, gastric lavage with iced tap water, for speed of cooling and efficacy of treatment in an anesthetized canine heatstroke model. Eleven mongrel dogs were anesthetized, shaved, and externally heated until core temperature reached 43.0 C (109.4 F). Control animals (n = 6) were cooled passively in room air. Treatment animals (n = 5) were cooled with the addition of gastric lavage with iced tap water through a large-bore orogastric tube. Temperatures were monitored using thermocouples in the brain, pulmonary artery, rectum, and subcutaneous tissue of the chest wall. Serial enzymatic and hematologic laboratory studies and hemodynamic parameters were measured prior to heating, at the end of heating, and at 0, 0.5, 1, 2, and 12 hours after heating. Animals were sacrificed 12 hours after heatstroke induction and gross and microscopic pathologic examination was performed. Central cooling rates achieved in the lavage group were five to six times faster than in the control group, (P less than .01) and are comparable with those reported in the literature for external cooling techniques. No significant complications were induced by tap water lavage. Rapid cooling in the lavage group resulted in a statistically significant improvement in serum creatinine and LDH after heatstroke induction (P less than .05). Gastric lavage with iced tap water appears to be an effective alternative or adjunctive cooling technique for heatstroke in the dog.