Results showed that three of the nine autistic subjects had an abnormally high plasma testosterone concentration (over two standard deviations above the mean for the comparison subjects), with values above that of the highest in the comparison subjects. Among the autistic subjects, plasma testosterone concentration values (ng/ml) were 0.64 for a prepubertal 10-year-old boy, 8.8 for the pubertal 17-year-old boy, and 0.5 for the pubertal 13-year-old girl, whereas the appropriate comparison group means were 0.06 (SD=0.03, range=0.01–0.15), 5.51 (SD=1.27, range=0.27–7.50), and 0.12 (SD=0.09, range=0.01–0.25), respectively. These three children all showed aggression against others. Thus, high plasma testosterone concentrations were present in all autistic subjects who exhibited aggression against others. The 10-year-old boy exhibited pubic hair growth. The 13-year old girl had a level of adrenal androgen (4.40 ng/ml) that was 500% higher than the mean level of the comparison subjects (mean=0.88, SD=0.39, range=0.36–1.70). The other autistic subjects showed normal adrenal androgen levels.