The individual iron sublattice magnetizations in yttrium iron garnet and gadolinium iron garnet have been measured by NMR techniques as a function of temperature. The observed resonance frequencies are slightly higher for GdIG in both cases, the differences at low temperatures being about 0.67 for the octahedral sites and 0.70 for the tetrahedral sites. These differences are tentatively interpreted as due to the volume dependence of the hyperfine coupling constant A. The difference for the octahedral sites decreases slightly with increasing temperature, while that for the tetrahedral sites increases appreciably. A molecular field calculation shows that this behavior can be explained by assuming that the Gd3+ ions interact much more strongly with tetrahedral sites than with octahedral sites. © 1963 The American Institute of Physics.