This research study investigates the effects of oxytocin and vasopressin on brain activity in adults with Autism Spectrum Disorders using functional magnetic resonance imaging (fMRI). Background: \- Oxytocin and vasopressin are two hormones produced in the brain. Both hormones can influence activity in brain regions such as the amygdala that are involved in social and emotional processing. There is evidence suggesting that oxytocin and vasopressin may be implicated in autism spectrum disorders (ASD). Objectives: -Here, we use functional magnetic resonance imaging (fMRI) to assess the effects of oxytocin and vasopressin on brain activity in adult healthy volunteers and adults with ASD. Eligibility: \- Right-handed individuals between 18 and 40 years of age who either have been diagnosed with autism, Asperger s disorder, or Pervasive Developmental Disorder- Not Otherwise Specified (PDD-NOS), or are healthy volunteers. Design: * This study requires 3 outpatient visits to the NIH Clinical Center in addition to a screening visit. Each visit will last about 2.5 hours. Participants may not smoke cigarettes or drink alcohol or caffeinated beverages for 12 hours before each visit. * During each visit, participants will receive a nasal spray that contains one of the following: oxytocin, vasopressin, or placebo. Participants will receive a different spray at each visit. * After using the nasal spray, participants will have an MRI scan of the brain while performing tasks with social and emotional stimuli. * After the MRI scan, participants will complete questionnaires about mood and reaction to the tasks, and will remain in the clinic until the effects of the study medication have worn off. * Participants will be contacted 1 day after each MRI scan for follow-up purposes.

Objective: The goal of this protocol, broadly stated, is to evaluate the effects of the neuropeptides oxytocin and vasopressin on the neural systems involved in social cognition and emotional processing in healthy volunteers and individuals with autism spectrum disorders (ASD). Study population: The research participants will be adult healthy volunteers and adults with ASD (ages 18-40 years). Design: This will be a double-blind cross-over functional magnetic resonance imaging (fMRI) study, requiring three visits in addition to a screening visit. At each visit, participants will receive an intranasal application of oxytocin, vasopressin, or placebo and will be scanned while performing social cognition tasks and tasks involving the processing of affective stimuli. Drug order will be randomized across participants in each group (healthy controls and individuals with ASD). Outcome measures: The outcome measures will include both performance scores and reaction times (RTs) on the behavioral tasks and changes in blood oxygenation level-dependent (BOLD) activation in the brain, in both healthy volunteers and patients with ASD. Our main brain region of interest will be the amygdala.