Coupling Constant Unification and LEP Data

The recent LEP data for gauge coupling constants constrain many grand unified models. In this paper, we study several possibilities for unification of gauge coupling constants. Without an intermediate mass scale, the minimal supersymmetric standard model is the only possibility. For one intermediate mass scale, it is possible to have many routes toward grand unification: $SO(10)\rightarrow SU(3)_c\times SU(2)_L\times SU(2)_R\times U(1) , SU(7), SU(8)$, etc. We present also simple relations for the possibility of unification.