A test rig was built to run steady-state experiments with air/water mixtures at low pressure (42 kPa), and to determine the performance characteristics of two-phase flow through a centrifugal pump. Application is to a loss-of-coolant accident situation in nuclear reactor power plants if a large break in one of the primary pump legs took place. Two feasible accident conditions were tested; first- (forward flow and rotation) and third-quadrant (reverse flow and rotation) conditions. A significant head-pump degradation process was observed in the first-quadrant operation for increasing amounts of gas supplied, whereas in the third quadrant no difference in performance was detected with respect to single-phase flow and up to an inlet volumetric quality of 20%. The data gathered have been correlated in terms of a defined head-loss ratio, flow coefficient, and volumetric quality, which facilitates its use in predicting pump performance in similar designs of different scale.