An improved understanding of the influence of fibers on the rheology of cementitious systems is needed so that fiber reinforcement can be used effectively. However, conventional rheometers are not suitable for testing stiff fiber-reinforced materials. In this study, a parallel plate rheometer that is capable of evaluating the rheology of stiff fiber-reinforced cement paste and mortar systems was designed and built. The governing equations for the rheometer were derived and experimental procedures were developed that yielded reproducible results. A comparative analysis of the custom-built parallel plate rheometer, a commercial rheometer and the values reported in the literature, indicated that the measurements obtained using the rheometer were reasonable. The, rheometer was then used to evaluate the rheology of a variety of cement paste systems, including stiff steel fiber-reinforced cement pastes. (C) 2006 Elsevier Ltd. All rights reserved.