Experimental results are presented on sputter-ion pumps of both Penning and magnetron configuration, into which thermionic electrons are injected from an auxiliary source.Empirical laws are established connecting the pumping speed, magnetic field strength, anode potential and pumping current.It is found that the injection of thermionic electrons allows the use of considerably lower magnetic field strengths and anode voltages than are required in a cold-cathode pump of the same pumping speed.The results show that as an ion pump the Penning structure is a more efficient electrode arrangement than a magnetron geometry.