There is a growing body of empirical evidence that suggests the importance of physiological factors for understanding relationship aggression. Several studies (Brumm, Rosenbaum, and Cohen, 1995; Cohen et al., 1995; Rosenbaum et al., 1994; Rosenbaum and Hoge, 1989; Warnken, Rosenbaum, Fletcher, Hoge, and Adelman, 1994) show that a history of head injury is a significant risk factor for relationship aggression and that abusive men can be reliably discriminated from non-abusive men on several measures of neuropsychological performance that corresponds to frontal-temporal lobe damage. Research in progress (Rosenbaum) is assessing differences in serotonergic functioning between batterers and non-batterers. Gottman et al. (1995) have shown that some abusers manifest differences in cardiac reactivity compared to non-abusers. Further research on these fronts, as well as on other physiological factors yet to be determined is needed. Based on research to date, the authors propose a biopsychosocial model of relationship aggression. Components of the model are factors that affect arousal which triggers factors that affect behaviors of high habit strength due to psychosocial conditioning. Factors that affect the threshold of aggression include alcohol or drug use, head injury/neuropsychological dysfunction, characterological low impulse control, and cognitions and stress. 69 references and 1 figure