Postherpetic neuralgia is one of the most troublesome diseases in pain clinics. The N-methyl-D-aspartate (NMDA) receptor antagonist, magnesium, reduces the level of neuropathic pain and hyperalgesia in patients with postherpetic neuralgia. Magnesium has been shown to exert a physiological block of the ion channel on the NMDA receptor, thereby preventing extracellular calcium ions from entering the cell and contributing to secondary neuronal changes. Accordingly, we attempted to administer a continuous intravenous infusion of magnesium, which resulted in a decrease in the VAS without side effects.