We present a theory for exciton and impurity states in semiconductors, which is valid for all values of the magnetic field. The formalism is based on the introduction of tensor operators and includes the effect of the exchange interaction. Accurate solutions forthe ground state are presented and compared with the results of a previous adiabatic method, which is valid only for very large fields. We show that the present analysis is superior to all previously used methods for all values of the magnetic field. © 1980.