Fifty-eight normal adolescent Swedish boys, aged 16, provided two sets of blood samples for plasma testosterone assays as well as data on a number of personality inventories and rating scales assessing aggression, inpulsiveness, lack of frustration tolerance, extraversion, and anxiety. Physical variables such as pubertal stage, height, weight, chest circumference, and physical strength were measured. There was a significant association (r = 0.44) between plasma testosterone levels and self-reports of physical and verbal aggression, mainly reflecting responsiveness to provocation and threat. Lack of frustration tolerance was also related to testosterone levels. About 40% of the variance in perfectly reliable testosterone measurements could be predicted from equally reliable Physical + Verbal Aggression and Lack of Frustration Tolerance scales. Pubertal stage was correlated with testosterone (r = 0.44), but the above-mentioned relationships could not be accounted for by pubertal stage as a third common variable. Previous hypotheses relating testosterone to strong body build and antisocial behavior, respectively, received only weak or no support.