In a recent series of publications, a new theory of electromagnetic radiation with emission frequency close to the plasma frequency and/or its harmonic (i.e., the plasma emission) was presented; In this theory, the emission of radiation takes place as a result of excitation of long wavelength modes by a nonlinear beam-plasma instability, which are converted to radiative electromagnetic waves by a nonlinear mode conversion process. Unlike standard theories, the new theory;predicts high radiation growth rate. In all the previous efforts on this theory, however, effects due to the presence of constant background magnetic field were ignored. The purpose of this article is to generalize the new theory to the case of weakly magnetized plasmas. (C) 1997 American Institute of Physics.