CP PHASES IN MODELS WITH SOME FERMION MASSES VANISHING AND OR DEGENERATE/

We count the number of CP breaking phases in models with SU(2)(L) x U( 1)(Y) and SU(2)(L)x SU(2)(R)x U(1)(B-L) electroweak gauge groups and e xtended matter contents with some fermion masses vanishing and/or dege nerate. Quarks and leptons, including Majorana neutrinos, are treated in a similar way. CP violation is characterized in the mass-eigenstate and in the weak-eigenstate bases. Necessary and sufficient conditions for CP conservation, invariant under weak basis redefinitions are als o studied in these models. CP violating factors entering in physical o bservables and only invariant under phase redefinitions are discussed.