Empirical analyses conducted within a causal-analytic framework (path analysis) on a sample of normal adolescent human males suggested that circulating levels of testosterone in the blood had a direct causal influence on provoked aggressive behavior (self-reports): A high level of testosterone led to an increased readiness to respond vigorously and assertively to provocations and threats. Testosterone also had an indirect and weaker affect on another aggression dimension: High levels of testosterone made the boys more impatient and irritable, which in turn increased their propensity to engage in aggressive-destructive behavior. Two somewhat parallel dimensions of behavior, intermale and irritable aggression, have been identified in animal research to be under testosterone control.