The state of the surface of poorly crystallized or amorphous (a-BN) and highly oriented hexagonal (h-BN) boron nitride before and after treatment in a hydrogen plasma has been studied by high-resolution Auger electron spectroscopy. Treatment of both modifications of BN in hydrogen plasma is found to lead to a partial transformation of sp(2) bonds into sp(3) bonds on the surface. This is thought to be a result of terminating dangling bonds of sp(2)-hybridized BN by hydrogen atoms. The formation of chemical N-H bonds after treatment of BN in hydrogen plasma is found on the surface of both a-BN and h-BN, whereas in practice, B-H bonds appear to form only on the treated surface of h-BN.