An optical anisotropy decay technique for measuring probe rotational times in glassy materials is presented. Rotational times from 10(1.4) to 10(5) s have been obtained for a molecule of 1-naphthyl-azomethoxybenzene (NAMB) in o-terphenyl (OTP) over a temperature range from T-g + 3.5 to T-g - 16.5 K. The rotational diffusion follows the temperature dependence of Debye-Stokes-Einstein down to T-g - 4 K with an activation energy of 320 +/- 30 kJ/mol. Below T-g - 9 K, the temperature dependence of rotation mobility was found to be much weaker with an activation energy of 70 +/- 15 kJ/mol.