The equilibrium acidities (PKHA values) in DMSO of the following hydroxylamines have been measured : (1) N-phenylhydroxylamine and its p-bromo and p-cyano derivatives, (2) N-benzyl-N-phenylhydroxylamine and its p-bromo and p-cyano derivatives, (3) O-benzyl-N-phenylhydroxylamine, (4) N-benzoylphenylhydroxylamine and its p-bromo and p-cyano derivatives, and (5) N-hydroxylpiperidine. The BDEs of the O-H and/or N-H bonds in these 11 weak acids have been estimated by combining their PKHA values with the oxidation potentials of their conjugate bases according to the following equation : BDE(HA) = 1.37 pK(HA) + 23.1 E(OX)(A(-)) + 73.3 kcal/mol.