Reportedly, galactose provides an alternative carbohydrate source and improved homeostatic regulation of glucose in the premature infant. Because of its potentially toxic effects, sensitive methods are needed for monitoring its concentration during therapy. We evaluated an immobilized galactose oxidase/hydrogen peroxide electrode system and a modified homogeneous enzymic method. Both methods are suitable for measuring galactose in a small sample and are comparably precise. The latter method gives superior analytical recoveries below 100 mg/L, but is linear in absorbance response to only 300 mg/L. We find the immobilized-enzyme method superior for monitoring treatment of neonates with galactose, because it requires only a few minutes and 25 microL of serum, and the analytical procedure is simpler.