The paper describes two particle feeders (fluidizing and entrainment): one was developed by modifying a design used for coal dust suspensions, and the other was developed later in response to shortcomings of the initial system. The two feeders were tested and compared for their performance at feeding Ca(OH)2 sorbents. The development and operation of a particle feeder for laboratory-scale, gas/solid-flow reactors is crucial in many research efforts. On this small scale, it is particularly difficult to feed particles at high mass rates without quantities of carrier gas that disrupt the operation of the reactor. These problems have been encountered in research programs involving the injection of limestone-based sorbents into utility boilers for the removal of SO2. The injection systems for these reactors must be designed to minimize the effects of the sorbent carrier gas upon the simulated utility boiler environment.