We evaluated the effect of full body restraint and rapid stimulus exposure (response prevention-flooding) on three Great Dane dogs, Canis familiaris , exhibiting high levels of aggression toward strangers or other dogs. We immobilized each dog in a restraint box by pouring grain in the box up to the level of the dog’s neck. Each dog was rapidly subjected to increasing intensity of the appropriate eliciting stimulus (adult, child, or dog) and responses were rated using a standardized numerical rating system. The dogs’ aggressive behavior diminished rapidly during restraint, and resulted in calm behavior during the highest stimulus intensity. Owners reported decreases in aggressive behavior for several months to years following the restraint sessions. Rapid stimulus exposure, when accompanied by complete response prevention, seems to result in large and long-lasting decrements in aggressive responses.