Serum magnesium concentration was measured in 80 adult patients (age range: 18-40 yr) presenting with acute, uncomplicated falciparum malaria infection and a control group of 20 age-matched, healthy individuals. The mean serum magnesium concentration in the patients was 1950.0 +/- 10.0 microg/dL. The control serum magnesium was 640.0 +/- 40.0 microg/dL. This represents an over threefold increase in serum magnesium levels above normal value, p < 0.01. The key pathogenic event in acute falciparum malaria infection is the hemolysis of both infected and uninfected red blood cells. Therefore, the increased serum magnesium concentration might occur because of the hemolysis arising from erythrocytic merogony because red blood cells contain high amounts of magnesium. In conclusion, the increased serum magnesium has potential application as a biomarker of acute falciparum malaria infection in adults.