Two novel rheological devices for measurements on hydraulic fracturing fluids have been developed. The helical screw viscometer (HSV) can be used to study the rheology of fracturing fluids such as crosslinked gels and proppant-laden slurries. The dynamic settling tester (DST) has been designed to measure proppant settling velocities in flowing hydraulic fracturing fluids. This paper will discuss the principles of the new equipment and its applications in the field of hydraulic fracturing. The HSV can be used e.g. to study the slurry rheology of fracturing fluids, the relation between the chemistry and flow mechanics of borate-crosslinked gels and the compatibility of resin-coated proppants and fracturing fluids. The DST has proved highly effective for studying the fundamental properties of the complex fluids typically used for hydraulic fracturing treatments. Completely unexpected phenomena - such as a decrease in proppant settling rates due to shear of a shear-thinning fluid — have been identified.