The diffusion of Fe2+ in garnets has been investigated using the optical absorption of the Fe2+ as a measure. Two annealing procedures have been investigated: (1) firing at 1200°C in pure N2 and (2) heating the sample in a sealed, evacuated quartz tube with zirconium as a getter. The unexpectedly high diffusion rates explain in part the rapid decay of the induced uniaxial aniso‐tropy with N2 treatment observed by LeCraw et al.