In the last four years near infrared spectroscopy (NIRS) has been used in cerebral functional activation studies to monitor changes in concentration of oxy-, deoxy- and total hemoglobin ([O 2 Hb], [HHb] and [tHb] respectively) in response to different stimuli. Previous studies were performed with a 1-2 Hz temporal resolution and a poor signal-to-noise (S/N) ratio. The aim of this study was to investigate the response of the motor cortex region during a finger opposition task in single subjects using a novel continuous wave NIRS instrument with enhanced temporal resolution and S/N ratio. Six subjects performed a sequential finger opposition task with the right hand (20 s duration; 2 Hz). The optodes were positioned over the left motor cortex region using an inter-optode distance of 3.5 cm. The high S/N ratio and 0.1 s sampling time allowed clear monitoring of [O 2 Hb] and [HHb] changes due to heart beat as well as to respiration. The contribution of the heart pulse to the total signal was less than 0.4%. As previously shown by others using pooled data, an increase of [O 2 Hb] during the activation accompanied by a decrease of [HHb] was found in most subjects for every activation cycle. Our approach provides a better insight into the underlying physiological mechanisms.