Magnesium and ionized calcium in mixed umbilical cord blood was assessed colorimetrically in 30 distressed and 30 healthy term newborn infants. Distressed infants with a severe or moderate degree of hypoxic-ischemic encephalopathy (HIE) (n = 20) had significantly lower (p < 0.001) concentrations of magnesium (0.52 +/- 0.08 mmol/L) compared to the control group (0.69 +/- 0.06 mmol/L). No differences in concentrations of ionized calcium between distressed and control infants were detected.