The spin-lattice relaxation times, T-1, in alpha-, beta-, and amorphous Si3N4 have been obtained for the first time, using a multiple-pulse saturation recovery method. The saturation recovery of the Si-29 magnetization follows exponential behavior under magic-angle spinning conditions, within the Limits of experimental error. A rather wide dispersion of T-1 values is observed for the phases of Si3N4: 284 +/-29 min (-46.686 ppm) and 260 +/- 23 min (-48,812 ppm) for the alpha-phase, 36 +/- 4 min for the beta-phase, and 11 +/- 1 min for the amorphous phase, assuming an exponential recovery. The values obtained for the exponent in the power-law fitting are 0,599(9) (-46.686 ppm) and 0.61(1) (-48,812 ppm) for the alpha-phase, 0.52(2) for the beta-phase, and 0.53(3) for the amorphous phase.