The role of magnesium as an analgesic in patients is unclear. Hypomagnesaemia is a common electrolyte abnormality, in the chronic state symptoms are insidious and often non-specific. It is often undiagnosed and thus untreated. There is evidence from animal studies that magnesium is involved in pain control including an animal model of hyperalgesia induced by hypomagnesaemia. We report two cases of patients admitted for pain control which improved when hypomagnesaemia was treated. Each case had metastatic cancer. Both were found on admission to have asymptomatic hypomagnesaemia and were treated with intravenous magnesium. Treatment for hypomagnesaemia resulted in an improvement in pain control such that analgesia was decreased. The incidence of hypomagnesaemia in palliative patients is unknown although it is thought to be common. These cases suggest that treating hypomagnesaemia may improve pain control.