There has been intensified interest in the neuropeptides oxytocin (OT) and 
arginine vasopressin (AVP) in autism spectrum disorders (ASD) given their role 
in affiliative and social behavior in animals, positive results of treatment 
studies using OT, and findings that genetic polymorphisms in the AVP-OT pathway 
are present in individuals with ASD. Nearly all such studies in humans have 
focused only on males. With this preliminary study, we provide basic and novel 
information on the involvement of OT and AVP in autism, with an investigation of 
blood plasma levels of these neuropeptides in 75 preadolescent and adolescent 
girls and boys ages 8-18: 40 with high-functioning ASD (19 girls, 21 boys) and 
35 typically developing children (16 girls, 19 boys). We related neuropeptide 
levels to social, language, repetitive behavior, and internalizing symptom 
measures in these individuals. There were significant gender effects: Girls 
showed higher levels of OT, while boys had significantly higher levels of AVP. 
There were no significant effects of diagnosis on OT or AVP. Higher OT values 
were associated with greater anxiety in all girls, and with better pragmatic 
language in all boys and girls. AVP levels were positively associated with 
restricted and repetitive behaviors in girls with ASD but negatively 
(nonsignificantly) associated with these behaviors in boys with ASD. Our results 
challenge the prevailing view that plasma OT levels are lower in individuals 
with ASD, and suggest that there are distinct and sexually dimorphic mechanisms 
of action for OT and AVP underlying anxiety and repetitive behaviors. Autism Res 
2013, 6: 91-102. © 2013 International Society for Autism Research, Wiley 
Periodicals, Inc.