AbstractThe syndrome of hypomagnesemia in patients receiving total parenteral nutrition (TPN) is well known. To determine particular high‐risk groups for the development of this syndrome, 26 consecutive patients on TPN were initially evaluated for serum magnesium (Mg) and followed at regular intervals. Seventeen had a diagnosis of solid tumor or hematologic malignancy (CA); nine had inflammatory bowel disease and/or small bowel fistulae (ID). All met the standard criteria for being malnourished – anergy, low serum albumin, and recent weight loss. During TPN, all patients received an average of 24 mEq of magnesium sulfate per day, and all had satisfactory anabolic response in terms of weight gain and increase in serum albumin. Ten patients had at least one magnesium determination below the lower limits of normal, and four of these developed symptoms of tremor which responded to increased amounts of magnesium in their TPN. Eight of these ten (80%) had a diagnosis of CA, and four of four (100%) of those requiring additional magnesium to alleviate symptoms had CA. None of the patients with ID developed symptomatic hypomagnesemia. We conclude that patients with solid tumor malignancy are more likely to develop hypomagnesemia, possibly because of the increased requirements for magnesium in lymphocytolysis of tumor cells, and they must be carefully monitored to prevent this complicat