-Perinatal asphyxia induces retinal lesions, generating ischemic proliferative retinopathy, which may result in blindness. Previously, we showed that the nitrergic system was involved in the physiopathology of perinatal asphyxia. Here we analyze the application of methylene blue, a well-known soluble guanylate cyclase inhibitor, as a therapeutic strategy to prevent retinopathy. Male rats (n Ï 28 per group) were treated in different ways: 1) control group comprised born-to-term animals; 2) methylene blue group comprised animals born from pregnant rats treated with methylene blue (2 mg/kg) 30 and 5 min before delivery; 3) perinatal asphyxia (PA) group comprised rats exposed to perinatal asphyxia (20 min at 37°C); and 4) methylene blue-PA group comprised animals born from pregnant rats treated with methylene blue (2 mg/kg) 30 and 5 min before delivery, and then the pups were subjected to PA as above. For molecular studies, mRNA was obtained at different times after asphyxia, and tissue was collected at 30 days for morphological and biochemical analysis. Perinatal asphyxia produced significant gliosis, angiogenesis, and thickening of the inner retina. Methylene blue treatment reduced these parameters. Perinatal asphyxia resulted in a significant elevation of the nitrergic system as shown by NO synthase (NOS) activity assays, Western blotting, and (immuno)histochemistry for the neuronal isoform of NOS and NADPH-diaphorase activity. All these parameters were also normalized by the treatment. In addition, methylene blue induced the upregulation of the anti-angiogenic peptide, pigment epithelium-derived factor. Application of methylene blue reduced morphological and biochemical parameters of retinopathy. This finding suggests the use of methylene blue as a new treatment to prevent or decrease retinal damage in the context of ischemic proliferative retinopathy. retina; nitric oxide; ischemic proliferative retinopathy; methylene blue; angiogenesis PERINATAL ASPHYXIA (PA) is one of the most severe problems in perinatology services across the world (9,15,23,27). PA generates a transient global hypoxia-ischemia status that damages the brain, spinal cord, and retina (14, 17, 39, 52). The degree and the length of perinatal asphyxia are decisive for the development of injury sequelae, such as attention-deficit hyperactivity disorder (1), epilepsy, mental retardation, spasticity, and visual or hearing alterations (61). One third of asphyctic neonates develop serious long-term neurological injuries including several degrees of ischemic proliferative retinopathy (IPR) and even blindness (20).In rats, the retina is particularly sensitive to oxygen alterations (56), and the morphological changes observed in its inner layers are compatible with some alterations observed in human diseases such as retinopathy in diabetes, retinal vein occlusion, and retinopathy of prematurity (ROP), an avoidable cause of visual impairment and blindness in children (20, 61). The changes observed in asphyctic animals include ganglion cell degeneration, n...