Rapid eye movement sleep deprivation is known to affect central neuronal excitability and responsiveness. Because chloride-sensitive Mg-ATPase is known to affect the neuronal transmembrane potential, this study was conducted to investigate if the enzyme activity might be affected on deprivation. The flower pot method was used for 2 and 4 days of deprivation and suitable control experiments were conducted. The enzyme activity was estimated in the microsomal preparation of the whole brain as well as in different areas of the brain in rats. The results suggested that the deprivation increased the enzyme activity although the chloride-insensitive Mg-ATPase activity remained unaffected. The increase in the enzyme activity is likely to reduce the neuronal hyperpolarization. The findings fit in with existing knowledge and help in explaining earlier observations.