Neonatal encephalopathy of early onset, plausibly related to hypoxia and ischemia remains one of the main problems in perinatal medicine. Efforts are necessary to find new non-invasive methods for assessing brain oxygenation. Near-infrared spectroscopy (NIRS) provides information on the concentrations of the oxygenated and reduced forms of hemoglobin, as well as the redox state of cytochrome aa3. Different important variables can be derived through hemoglobin measurement, such as cerebral blood volume and flow, and the responses of these to changes in pCO2. Changes in cytochrome aa3 may provide immediate information on intracellular oxygen utilization. Various studies have shown the feasibility of NIRS in preterm infants. Methodological and technical problems of this method are discussed.