Cinici E, et al. – The investigation intends to assess changes in neopterin levels and tryptophan degradation which are induced by Th1–type immune response and nitric oxide metabolism which may be involved in allergic inflammation. This preliminary examination shows that serum nitric oxide metabolism could have a role in allergic conjunctivitis. Serum neopterin levels but not tryptophan metabolism could serve as a biomarker in patients with seasonal allergic conjunctivitis.