Autism spectrum disorders are complex developmental disorders with increasing incidence and poorly understood etiology. Imbalance of amino acids profoundly influences brain function, and is thought to be one of the key players in the pathophysiology of autism. This study aimed to measure the plasma amino acid profiles of 20 Egyptian and 20 Saudi autistic patients in comparison to matching healthy controls to clarify the role of impaired amino acid concentrations in the etiology of autism. Plasma amino acids profiles were measured using high performance liquid chromatography. While plasma levels of glutamic, aspartic, and glycine recorded the most significant percentage elevated amino acids, glutamine, asparagine, arginine, tyrosine and isoleucine recorded the most remarkable percentage decrease in autistic patients from both populations compared to controls. Among the calculated relative values, only acidic/basic, and glutamate/glutamine ratios were significantly higher i n autistics compared to controls. Non-essential/essential and glucogenic/ketogenic ratios were unaltered in autistics compared to controls . Increased plasma glutamate/glutamine ratio, together with increased glycine, arginine, aspartate, aspargine levels , and acidic/basic amino acid ratio can serve as a predictive tools for the early detection of autism. These findings suggest that gl u- tamatergic abnormalities in the brain may be associated with the pathobiology of autism.