Abstract Measurements of T 1 for 57Fe nuclei in Yb-doped YIG are reported for the temperature range 0·7–140 K, with the magnetization along the , , , and  crystallographic directions respectively. The dependence of T 1 on Yb concentration and on the magnitude of the applied field was also studied. These results are interpreted in terms of the ‘slow relaxation theory’, and are correlated with the ferrimagnetic resonance work of Clarke, Tweedale, and Teale, whose data have been reanalyzed by us. Both sets of data can be represented fairly well by the theory, with a consistent set of relevant parameters. However, the tensor G which describes the splitting of the Yb ground-state doublet must be modified somewhat from that deduced by Clarke et al., the new principal values being G 1 = 29·0 cm −1, G 2 = 20·4 cm −1 and G 3 = 8·5 cm −1 respectively. Below approximately 10 K, when the magnetization is in the  or  direction, the nuclear relaxation rate is higher than predicted. These anomalies correspond to those observed in ferrimagnetic resonance line width, which have been attributed to Yb ions on the octahedral lattice sites normally occupied by iron. Anomalously large values of T −1 1 are also observed below approximately 4 K in the  and  directions, and these remain to be accounted for.