Serum magnesium in Greenland Eskimos living in Greenland is significantly higher (p less than 0.001) than in Greenlanders and Danes living in Denmark. Danes living in Greenland show intermediate values. The higher serum magnesium may be due to a high intake of nutrients from fish and sea mammals. A more complete intestinal absorption of magnesium caused by a low dietary calcium should also be considered. The high serum magnesium may contribute to the rare occurrence of urinary calculi in Greenlanders.