  Within the supersymmetric SO(10) grand unified theory (GUT), a new mechanism,
giving the light Higgs doublet as a pseudo-Goldstone mode, is suggested.
Realizing this mechanism, we present an explicit model with fully realistic
phenomenology. In particular, desirable symmetry breaking and natural all-order
hierarchy are achieved. The constructed model allows one to have a realistic
fermion pattern, nucleon stability, and successful gauge coupling unification.
The suggested mechanism opens prospects in the field for a novel $SO(10)$ GUT
model building and for further investigations.
