Abstract – There are many problems connected with aggressive dogs and often these problems are the reason for the animal neglect. The aim of this study was to evaluate, with a specific test, the temperamental traits of 2 groups of biting kennel and pet dogs. The test has been divided into 4 phases: approach and interaction with a strange person, with a doll, with a false dog and the possession for food. Among kennel biting dogs and pet ones differences have been found regarding their reactivity, agonistic and fear behaviors and therefore their sociability towards different kinds of stimuli. A specific questionnaire submitted to pet dog owners turned out to be a sensitive instrument of differentiation between groups, in particular with reference to behaviors related to aggressiveness.