The gas calibrations of the Explorer 32 satellite atmospheric density experiment provided comparisons of the operation of the following five kinds of ionization gauges: (1) flight type, glass enveloped, cold cathode, magnetron gauge (model NRC-528), (2) flight type, metal enveloped, cold cathode, magnetron gauge (model GCA-R5), (3) commercially available, glass enveloped, “Redhead gauge” (model NRC-552), (4) flight type, metal enveloped, warm cathode, magnetron gauge (WCM), and (5) commercially available, metal enveloped, Penning-type gauge (model GE-22GT210).The nitrogen pressure responses of these gauges are compared in terms of the conversion constant (C). C is the ratio of the cathode current to the pressure and is related to the number of ions produced per neutral particle in the gauge. The 552 and R5 gauges exhibit values of C which axe maximum between10−10and10−9Torr and decrease at higher pressures. In contrast to this behavior the 528 and 22GT210 gauges exhibit primarily increasing C values with pressure, and the C values of the warm cathode magnetron are constant at low pressures. Experimental results which can be interpreted in terms of the behavior of the negative space charge in the gauges are briefly discussed. A high sensitivity of the R5 gauge response characteristics to anode voltage is demonstrated in terms of C values, oscillation regions, and discontinuities.