E.P.R. of MnO₄^2- centres in KBr single crystals has been investigated at 9·5 and 35 GHz in the temperature range 1·6-77 K. At 4·2 K, the spectrum exhibits a more nearly cubic anisotropy. A temperature variation study indicates that the spectra disappear reversibly above about 8 K. Uniaxial stress measurements at X-band have shown the importance of random strain.