Molecular genetic analysis of complex traits such as aggression strongly depends on careful phenotyping of individuals. When studying canine aggression, the information provided by the owners of the dogs is often not detailed and reliable enough for this purpose. Therefore we subjected 83 golden retrievers, both aggressive and nonaggressive individuals, to a behavioral test. These tests were analyzed with help of an ethogram, resulting in a behavioral profile for each of the dogs. In this article three methods are described of converting these profiles into a measure of behavioral phenotype. The usefulness of the methods is evaluated by comparing the test results with information provided by owners. Moreover, the hypothesis underlying all these methods, that a lowered threshold for aggressive behavior in general is present in the dogs, is also evaluated. Future research will need to reveal whether the methods meet the high standards that are necessary for studying complex traits.