BACKGROUND: During intracranial brain surgery, numerous factors may alter cerebral blood flow and the oxygen supply-demend balance. Continuous monitoring of the jugular bulb venous oxygen saturation (SjvO2) may help in the anesthetic management of such procedures. METHODS: Fiberoptic SjvO2 was continuously monitored and recorded 1, 3 and 5 min after the skin incision, skull bone craniotomy, dura open and dura closure in 20 patients. RESULTS: The SjvO2 was increased after the skin (scalp) incision at 1, 3 and 5 minutes and also after endotracheal suctioning for removal of secretions. CONCLUSIONS: Although the accuracy of Fibroptic SjvO2 determination is limited, it allows the detection of cerebral blood flow and oxygen supply-demend imbalance during brain surgery. The frequent occurance of SjvO2 elevations is suggestive of reactive hyperemia mechaniams.