We report the results of 1 1 B spin-lattice relaxation studies of SrB 6 , EuB 6 and LaB 6 at low temperatures. The temperature and field dependencies of the spin-lattice relaxation rate T 1 - 1 follow the expectation for a simple metal only for the case of LaB 6 . Although the charge carrier concentration in EuB 6 is at least two orders of magnitude smaller than in LaB 6 , its relaxation rate at 20 K is about five orders of magnitude larger, and is attributed to fluctuations of the Eu moments. In spite of an again much smaller charge carrier density, T 1 - 1 of SrB 6 at 20 K is close to that of LaB 6 . A cross-over or phase transition phenomenon below 0.5 K previously indicated by specific heat and resistivity data, is also reflected in T 1 - 1 (T) of SrB 6 .