Modifications in neurotrophins, neuropeptides, cytokines and nitric oxide (NO) levels in autism may represent different biological aspects of the disease. In the present study we investigate simultaneously all these variables as an attempt to clarify their interrelationships in autism. Plasma levels of vasoactive intestinal peptide (VIP), neurotrophin-3 (NT-3), cytokines and nitric oxide (NO) were determined in children with DSM-IV autistic disorder (n = 24) and in age- and gender-matched healthy controls (n = 24). VIP, NT-3, IFN-γ and IL-1β levels were measured by ELISA, TNF-α, IL-10, IL-6, IL-4, IL-2 were evaluated by fl ow cytometry, and NO by Griess reaction. Plasma levels of VIP, IFN-γ and NO were significantly higher and NT-3 plasma levels were significantly lower in children with autism, compared to the healthy subjects. In children with autism there was a positive correlation between plasma levels of NO and IFN-γ. Our results indicate the presence of altered levels of neurotrophin and neuropeptide in infantile autism and provide additional evidence that higher levels of IFN-γ may be associated with increased oxidative stress in autism. © Georg Thieme Verlag KG Stuttgart · New York.