Various sites may be used to obtain blood (plasma) for the determination of the glucose concentration in the neonate. Because multiple sites may be sampled in the same neonate, it is important to determine the variability in blood glucose concentration which may result from such sampling. Since pain and mechanical forces may be different because of the method used to obtain the capillary (heelstick) blood compared to the venous specimen, the two sites were sampled, and the blood glucose concentration was determined simultaneously in 25 asymptomatic well neonates whose mean birth weight was 2,562 ± 152 g and whose gestational age was 35.5 ± 1.5 weeks. There was a significant (p < 0.0001), but relatively weak correlation (r² = 0.64) between capillary (heelstick) blood and venous blood relative to blood glucose concentration. When the capillary (heelstick)-venous glucose concentration difference was compared to the mean of the capillary (heelstick) and venous glucose concentrations, a difference of ± 0.5 mM (9 mg/dl) was noted in 3 of 25 neonates. Appropriately obtained capillary (heelstick) blood samples provide measurement of blood glucose concentration which are variable compared to venous samples, but which are probably not significant physiologically.