The paper reports on experiments performed by the author at the Hydraulic Laboratory of the University of California with the equipment furnished by the Byron Jackson Company, Berkeley, Calif. Factors governing leakage loss and means to reduce leakage loss were studied. With a special pump, leakage was measured under actual operating conditions, using wearing rings of various types, width, and clearances. Tests were performed at four speeds and different heads. The results are presented in the form of curves, the coefficient of discharge through the clearances being plotted as ordinates against pressures at the wearing ring as abscissas. To facilitate the calculation of the pressure at the wearing ring the pressure distribution in the pump case was studied and an approximate formula was developed. The axial thrust in single- and multi-stage pumps was measured with a specially designed thrust bearing which indicated the thrust directly in pounds under actual operating conditions. New sources of thrust were established—those caused by unequal pressures on the impeller shrouds from the inside due to various causes, the most important of which are an uneven radial velocity distribution and cavitation. In multi-stage pumps, with impellers mounted back to back, generally considered balanced on account of symmetry, it was discovered that there is considerable axial thrust produced by unequal pressures in adjacent stages acting upon the shaft shoulders and impeller hubs extending through the walls of the adjacent stages. Means to eliminate this thrust were found.