We examine a superpotential for an SO(10) GUT and show that if the parameters of the superpotential are in a certain region, the SO(10) GUT has an intermediate symmetry SU(2${)}_{\mathit{L}}$\ensuremath{\bigotimes}SU(2${)}_{\mathit{R}}$\ensuremath{\bigotimes}SU(3${)}_{\mathit{C}}$\ensuremath{\bigotimes}U(1${)}_{\mathit{B}\mathrm{\ensuremath{-}}\mathit{L}}$ which breaks down to the group of the standard model at an intermediate scale ${10}^{10}$--${10}^{12}$ GeV. In the model, by the breakdown of the symmetry, right-handed neutrinos acquire a mass of the intermediate scale through a renormalizable Yukawa coupling. \textcopyright{} 1996 The American Physical Society.