Autism spectrum disorder (ASD) affects people from all regions of the globe, regardless of nationality, living standards or social group. Currently, it is assumed that ASD pathogenesis is multifactorial because there is no one specific cause of the disorder. According to literature, ASD may result from genetic defects, metabolic disorders or exposure to environmental factors. There is a number of hypotheses that attempt to explain the intensity of emotional and behavioral symptoms or the increased sensory threshold that is characteristic of ASD. It is suggested that neurological changes may be due to oxidative stress occurring in early brain tissue development and reduced antioxidative barrier. Due to the abnormalities in the synthesis of neurotransmitters, often occurring in ASD, autism is investigated for disorders of vital biochemical processes of methylation and transsulfuration. Finding a biomarker for a disturbed oxidative-reduction equilibrium, methylation pathway pathology, or other reason could be an important diagnostic tool and the base for individual treatment for patients with varying degrees of severity. This work provides a review of the potential biological indicators for ASD taking into account the occurrence of oxidative stress and the methylation and transsulfuration cycles