ABSTRACT Fatty acid supplements are among the most popular complementary products consumed by children with Autism Spectrum Disorder (ASD), driven by anecdotal evidence of benefit and a few small RCTs that demonstrated improvements in externalizing behaviors. Because no approved drugs exist to treat the core symptoms of ASD, well-intentioned parents are reaching for any product that may help their child. The implications are that fatty acid supplements are given to children without any evidence base as to their function, mechanism of action, effective dose, or benefits versus harms. Over-the-counter (OTC) fatty acid supplements are plentiful and consist of varying fatty acid compositions and often contain other ingredients. Recent evidence from our group and others suggest a combination of fish and borage oils providing supplementation of DHA, EPA and GLA (?Omega 3-6?) is particularly promising compared to other formulations. A critical need exists to evaluate Omega 3-6 for optimal dosing and changes in a physiologically relevant biological signature related to ASD symptoms, before a rigorous, full-scale efficacy trial can be launched. Our objective is to evaluate the effects of higher doses of Omega 3-6 on pre-specified biological signatures? Our overall hypothesis is that optimal dosing of Omega 3-6 will alter biological signatures in a manner that correlates with improvements in ASD-related behaviors. The R61 phase of this proposal will test the hypothesis that Omega 3-6 will produce a clinically-significant reduction (improvement) in one or more the inflammatory markers IL-1?, IL-2, and IFN? and our higher doses will demonstrate bioavailability, safety, and tolerability. The R33 phase of this proposal will test the hypothesis that the impact on biological signatures correlates with Omega 3-6 dose, can be replicated in a new sample of patients, and the change in key inflammatory marker(s) are correlated with core ASD symptoms after supplementation. Upon completion of this proposed 2-phase project, we expect to have identified an optimal dosing range for which Omega 3-6 exerts its effect on inflammation and, subsequently, on ASD symptoms in children. Such results are expected to have an important positive impact by laying the necessary groundwork for a full-scale efficacy trial to evaluate the effect of Omega 3-6 on ASD symptom improvement.