Abstract The effect of in-plane magnetic fields on the carrier energy dispersion, mass enhancement and the photoluminescence line-shape is investigated in semiconductor quantum wells. Exact results are obtained for parabolic quantum wells. An accurate numerical method applicable for arbitrary confinement potentials is introduced. This technique, based on a plane-wave basis set, is applied to the square-well potential. Minimum-photoluminescence-energy data are presented as a function of magnetic field. The theoretical results yield reasonable agreement with the data.