Human intraspecies aggression can be defined as a broad sequential pattern of psychic experience and/or behavior, the goal response to which is to deliver stimuli suitable to damage the integrity of a social partner, the subject itself, or a surrogate-object. This article reviews work concerning human aggression, auto-aggression (suicide) and the role of central serotonin. The impact of a "high-risk - low 5-HIAA group" upon clinical psychiatric practice is discussed. Damaging and self-destructive experience and behavior and its biochemical aspects are regarded as a dysbalance syndrome causing well-defined vulnerability, which, in turn, becomes the basis of the psychopathology and psychodynamics of phenomena like aggression.