Genetic, neurobiological, neurochemical, environmental factors and their interactions contribute to autism phenotypes. Blood from 48 (age range: 4-17) autism spectrum disorder diagnosed patients (ASD) and 38 age- and gender-matched healthy control subjects was analyzed for numbers of neutrophils, lymphocytes, monocytes, albumin, serum Ischemia-Modified Albumin (IMA) levels and myeloperoxidase activity. The serum IMA levels, myeloperoxidase activity and peripheral blood mononuclear cells count were significantly higher in ASD cases than in the control subjects. There were no significant differences in albumin levels between the patient and control groups. These results suggest that the immune system, oxidative stress and myeloperoxidase activity may be activated in ASD. There is a clinical benefit from the early detection of ASD using myeloperoxidase activity, IMA levels and monocyte counts.