&NA;A new technique, laser‐Doppler flowmetry, has been used intraoperatively to measure blood flow responses in normal brain tissue and brain tumor to blood pressure and arterial blood gas alterations. We have observed that blood flow is reduced in most cerebral tumors, and that most tumors retain the normal response to changes in arterial blood gas; however, these responses are varied. One group of tumors in our study demonstrated an autoregulatory capacity; a second behaved passively—that is, blood flow changes followed blood pressure—while a third showed no response. (Neurosurgery24:166‐170, 1989)