In healthy human adults, cerebral concentrations of oxygenated hemoglobin ([HbO2]) and deoxygenated hemoglobin ([HbR]) were assessed during brain activation using near infrared spectroscopy (NIRS). Measurements were made either in the frontal cortex (n = 10) during performance of cognitive tasks or in the occipital cortex (n = 6) during visual stimulation (flash-light exposure, picture observation). The typical findings during brain activation were an increase in [HbO2] and a decrease in [HbR]. We demonstrate that these findings are not due to alterations in skin blood flow. NIRS is a simple bedside technique for the assessment of hemodynamic alterations accompanying brain activation.