The majority of studies attempting to evaluate the roles of hormones and neurochemicals in "aggression" concern laboratory rodents, notably rats and mice, with fewer investigations on infrahuman primates. Studies suggest that situations used to assess aggression (e.g., social conflict tests, parental attack, predatory behavior, use of unavoidable electroshock) actually tap a diverse range of motivations whose functions include offense, defense and predation. It is also apparent that ethoexperimental techniques, i.e., those applying ethological methodologies and concepts to laboratory situations, have advantages in assessing the direct and indirect consequences of chemical treatments. In this review, the impacts of hormonal manipulation (by surgery and/or application) and varying neurotransmitters (studied in terms of regional changes and as consequences of drug treatments) on a variety of forms of behavior are assessed. Different tests do show varying responses to common treatments, confirming the heterogeneity of the available paradigms. A brief discussion is provided of which tests are likely to prove most relevant to clinical studies.