Abstract Resonant light scattering has been shown to be a sensitive and versatile technique for the study of two-dimensional electron systems in semiconductors. We have extended the technique by the imposition of strong magnetic fields perpendicular to the two-dimensional planes in modulation doped AlGaAsGaAs heterostructures. At modest magnetic fields, the polarized spectra show a line which we interpret as forbidden cyclotron resonance, and a higher frequency mode probably interpretable as the upper hybrid or magnetoplasma mode. Both modes represent in-plane motion: scattering from in-plane degrees of freedom has not been observed in zero field. No known theory accounts for these observations. We summarize these results, and then discuss the properties of the magnetoplasma mode, suggesting its importance in the study of two-dimensional electron ordering at high fields.