Nuclear acoustic resonance has been investigated in single-crystal aluminum over a broad range of acoustic power. Saturation of both absorption and dispersion signals was observed. The shape and width of the absorption signal were found to depend on the acoustic power level. The line was found to either narrow or broaden with increasing acoustic power, depending on the magnitude of the low-frequency modulation field. the linewidth and shape changes were accounted for by the theory of Provotorov as expanded by Goldman, and Revokatov, and Lyapukhov. The signal intensity was found to decrease rapidly at high acoustic-power levels. This decrease is not accounted for by the above theories.