The possibility of directly separating and measuring the impurity and lattice contributions to nuclear spin-lattice relaxation under the condition of a steady-state magnetic saturation is demonstrated in the particular case of 27Al nuclei in a ?-irradiated ruby crystal. Contributions from trivalent and charge-exchanged chromium ions to impurity nuclear relaxation were separated. The number of charge-exchanged chromium ions was found. The spin relaxation time of Cr4+ centers was estimated. ? 1998 Academic Press.