Both photoproduction and photobleaching of dangling bonds by uv irradiation and thermal annealing were observed by electron spin resonance (ESR) in amorphous hydrogenated boron nitride. A model involving long-range hydrogen diffusion and hydrogen evolution is proposed to account for the ESR spectral line shapes observed after uv irradiation and thermal annealing. A Gaussian distribution of activation energies for the long-range hydrogen diffusion was used to explain the observed decrease in spin susceptibility after thermal annealing. A best fit to the spin susceptibility data gave an average activation energy of 0.0475 eV and a half-width of this Gaussian distribution of 0.027 eV.