Total residual chlorine (TRC) analyzers were selected as the first category of instrumentation to be evaluated by the recently incorporated Instrumentation Testing Service, Inc. Four commercial analyzers, representative of the major technologies available to measure TRC, were tested according to a rigid test protocol designed specifically to evaluate analyzer performance under controlled conditions. Significant differences in the performance of the four analyzers were identified--differences pertinent to the procurement of a specific instrument for a particular application. Bench-scale tests are a useful screening device before field testing and can lead to improved instrument design and performance.