This protocol is a blinded randomized controlled study of the effects of BB-12 with LGG at different doses in 70 healthy children with autism spectrum disorders at lower and higher doses over an 56-day period and a 28- day observation period. The study is being conducted in order to assess safety and tolerability of the probiotic (BB-12 with LGG) at 2 different doses of BB-12 with LGG. Identifying effects on behaviors in healthy children with ASD using SRS-2 and ABC, GI symptoms using GI symptom severity index, and relevant biomarkers of inflammation, microbiota, and metabolites. Primary testing and procedures will be conducted at the University of Texas Health Science Center at Houston and Memorial Hermann.

Biomarker identification includes Integrative analysis of plasma metabolome and stool microbiota will be conducted with the collaboration of Dr. Ruth Ann Luna and Dr. Jim Versalovic at Alkek Center for Metagenomics and Microbiome Research, Department of Molecular Virology & Microbiology of Baylor College of Medicine.

Inclusion Criteria:

• Healthy children with autism spectrum disorders (4 - 16 years old) and gastrointestinal symptoms, based on the GI Severity Index, with no other recognized illness will be enrolled in this study. There will be no selection on the basis of age, race, or gender. Although the investigators anticipate the majority of subjects will be male and/or pre-pubertal, in females of childbearing potential, a pregnancy test (urine) will be performed on females participating (at each visit).

Exclusion Criteria:

• Pregnancy or breastfeeding
• Subjects taking immunosuppressive medications, including oral corticosteroids
• A History of Positive result of HIV, Hepatitis B, and/or Hepatitis C test
• Abnormal lab test results (Section 5.2)
• Gastrointestinal diseases such as celiac disease, inflammatory bowel disease
• Subjects with an allergy to antibiotics
• Presence of fever or a pre-existing adverse event monitored in the study
• Use of probiotics in the last 30 days
• Acute diarrheal illness within the past 30 days
• Recent (within 2 weeks) or current use of oral antibiotics /anti-fungals Current use of oral laxatives
• Subjects with implanted prosthetic devices including prosthetic heart valves
• The investigators will require that subject not take any other probiotic-containing products, including yogurt supplemented with probiotics during the study period.

The head statistician and study pharmacist will be aware of randomization scheme. The investigators will use an adaptive minimization program for randomization that balances the 3 study arms with respect to distributions of sex and age (4-10 vs. 11-16 y.o.). Patients will be randomized to placebo, 1 billion CFU, and 10 billion CFU study arms at a ratio of 1:2:2. (Currently marketed over-the-counter probiotics typically contain 0.1-50 billion CFUs per dose.) The performance of our covariate adaptive randomization algorithm will be verified through simulation studies before implementation.