This paper proposes to deal with the problem of measuring the performance of centrifugal pumps in the field: How much liquid is being delivered at what pump head and at what efficiency or energy input? Emphasis will be on practical problems in the field associated with system balance or system performance for space heating and cooling and service water applications. While some reference will be made to pump testing in the factory as a guide to the principles involved, the basic discussion will be limited to field testing which is necessarily more approximate than shop or laboratory testing. In addition to discussing field testing of pumps, some suggestions will be made for identifying other problems which may be related to pump performance and which must be eliminated before pump performance can be determined.