It is important that dog owners, whether the dogs are pets, police, therapeutic, show or rescue dogs, know their natural communication. This can help to identify or reduce the possibility of unwanted aggressive behaviour toward the owner, strangers, or another dog. The aim of the BSc thesis was to analyse the aggressive behaviour of dogs through a socially acceptable behaviour test. The testing took place on an outdoor training ground consisting of 16 different tasks designed to elicit aggressive behaviour from the dog. Two groups of dogs participated in the test; 16 aggressive police dogs and 15 dogs without a history of aggressive behaviour. The dog guide was present in half of the tasks, and he was absent in the other half, in order to elicit from the dog a different response to the same stimuli. The test was recorded and evaluated using an ethogram with 28 forms of behaviour that fell into 6 categories: form of movement, posture, aggression, fear and stress, interaction with people, and other behaviours. Aggression was assessed on a 3-point scale and fear on a 5-point scale. As expected, we found out that police dogs would express a high level of aggression in the test, and that rescue and show dogs would respond non-aggressively (p = 0.002). In the degree of fear it was no statistically significant difference (p = 0.19).