We measured15O water uptake and [18F]fluorodeoxyglucose (FDG) uptake in four depressed individuals before electroconvulsive therapy (ECT) and 24 h after completion of a series of six to 11 bilateral ECT treatments. Studies of radioactive uptake were done using positron emission tomography, with FDG as a measure for glucose metabolism and with oxygen-15-labeled water as a measure for cerebral blood flow. The four patients showed decreased uptake of FDG in the frontal cortex after ECT treatment. Two of the three patients in whom15O water was measured showed decreased uptake in the frontal cortex after ECT.