Neuropeptide Y (NPY) has emerged as a novel peptide to antagonize various physiological consequences of stress within a mammalian brain. Hypoxia induced neuropeptide Y release in mammalian systems is well established. However, the possible role of NPY in regulating the effects of oxygen variation in lower vertebrates has not been investigated. We have studied the distribution and neuro-anatomical expression of NPY in the brain of Euphlyctis cyanophlyctis tadpoles, exposed to normal and reduced oxygen levels using immunohistochemistry. Animals exposed to hypoxia (<2mg/ml) exhibited a significant amplification of NPY-immunoreactivity throughout the brain. Increased NPY-ir perikarya appeared in all the sub-divisions of pallium, septum and preoptic area of telencephalon; suprachiasmatic nucleus, central and lateral thalamus, infundibulum and habenular regions of diencephalon; and nucleus cerebella and medulla of rhombencephalon. Most of these regions form the stress and anxiety regulating centers of a vertebrate brain and some of the parallel regions also respond to respiratory reflexes in mammals. Hence, our results suggest NPY induced modulation of hypoxia in Euphlyctis cyanophlyctis tadpoles.