Inclusion Criteria:

• Male or female from 2 years to 18 years of age (up to, but not inclusive of the 18th birthday)
• Diagnosis of autistic disorder corroborated by an Autism Diagnostic Interview - Revised (ADI-R) assessment performed by a certified investigator
• Physician Clinical Global Impression of Severity (of Autistic Disorder)
• History of chronic, persistent gastrointestinal disturbance
• No elective changes in medication, diet intervention, or behavioral therapy during the study (18 weeks total)

Exclusion Criteria:

• Evidence of a gastrointestinal infection or GI abnormality
• A known diagnosis of other gastrointestinal pathology
• Antibiotic and/or antifungal (e.g. nystatin) medication
• Chelation therapy
• Medication affecting gastrointestinal transit
• Planned use of prohibited drugs or agents that could affect GI transit
• Changes in diet intervention within 30 days prior to the screening visit
• Changes in alternative medical therapies or dietary supplements within 30 days prior to the screening visit
• Adding and/or changing behavior modification or psychotherapy during participation in the study
• Adding or changing psychotropic medication during participation in the study
• DSM-IV diagnosis of a pervasive developmental disorder other than autistic disorder
• Evidence of a seizure disorder, diagnosis of fragile X syndrome, tuberous sclerosis complex, liver disease, pancreatic disease, cystic fibrosis, or chronic infection
• Previous gastrointestinal surgery
• Pregnancy
• Participation in another investigational study
• Significant deviation from normal laboratory test values at baseline
• IgA deficiency (serum IgA < 5 mg/dL)
• A history of severe hypersensitivity to human immunoglobulin
• Treatment with any human immunoglobulin and/or immunoglobulin products
• Any concurrent medication that would compromise subject's tolerance of drug or compliance with the protocol