Proton spin-lattice relaxation data are presented for several plasma-deposited amorphous silicon-hydrogen films when (i) homonuclear dipolar interactions are suppressed, (ii) deuterium is isotopically substituted for hydrogen, and (iii) films are annealed. These data are consistent with a model in which proton nuclei are relaxed by hydrogen-containing disorder modes. Analysis of these data shows that the density of disorder modes is 30% higher in the low-hydrogen-density domain and that more than one hydrogen nucleus is associated with each disorder mode. The behavior of T1 upon annealing indicates that a small fraction of unpaired spins or "dangling bonds" may be associated with disorder modes. These results suggest that the role of hydrogen in amorphous silicon is more complex than passivation of dangling-bond intrinsic defects. © 1981 The American Physical Society.