The excitons in semiconductors with arbitrarily complex band structure are investigated within the framework of the effective mass approximation. The influence of homogeneous external fields on excitons is studied. The formulas for the coefficient of one-photon and two-photon absorption in the presence of homogeneous fields are derived. Some particular cases are considered. The theory developed is applied to the explanation of one-photon and two-photon absorption spectra in CuCl crystals.