This study used a multiple physiological systems measurement approach to test the hypothesis that asymmetry between the major components of the psychobiology of stress is associated with atypical behavior in youth [Bauer, A.M., Quas, J.A., Boyce, W.T., 2002. Associations between physiological reactivity and children's behavior: advantages of a multisystem approach. J. Dev. Behav. Pediatr. 23, 102-113]. Adolescents (N=67; ages 10-14; 52% male) provided 2 saliva samples before, and 4 samples after, a modified Trier Social Stress Test (TSST; Kirschbaum, C., Pirke, K., Hellhammer, D.H., 1993. The "Trier Social Stress Test": a tool for investigating psychobiological stress responses in a laboratory setting. Neuropsychobiology 28, 76-81). Samples were assayed for cortisol (C) and alpha-amylase (A-A), a surrogate marker of sympathetic nervous system (SNS) activity. Parents/guardians and adolescents reported on adolescents' aggressive behavior. Both salivary A-A and C increased in response to the TSST, with a peak response for A-A immediately post-TSST and for C 10 min post-TSST. A-A and C stress reactivity were estimated using area under the curve (AUC). Asymmetrical C and A-A reactivity accounted for 7% of the variance in parent-reported adolescent aggression. At lower levels of A-A reactivity, lower C reactivity corresponded to higher aggression ratings, but at high A-A reactivity levels, C reactivity was not related to aggression. These results support the hypothesis of Bauer et al. and underscore the importance of a multiple systems measurement approach in biosocial models of adolescent aggression.