Cerebral blood flow measurements are crucial for studying neuronal activity and cerebrovascular responses. Most optical techniques for monitoring real time blood flow rely on laser Doppler measurements which are limited to a localized region in space (point measurements). We have used the time-varying speckle pattern produced by coherent light scattered from moving particles to provide real time, two-dimensional maps of capillary blood flow dynamics. The speckle images of relative blood flow during cortical spreading depression showed a 2-3 mm area of increased blood flow propagating with a velocity of 3.5 mm/min. The speckle technique therefore, provides a relatively simple method of obtaining spatially resolved cerebral blood flow changes in the exposed cortex with high temporal resolution (milliseconds).