The absorption coefficient of GaAs-AlxGa1-xAs superlattices in an in-plane magnetic field is studied in the case of intraband transitions between electronic magnetic levels. A detailed analysis of the absorption peaks and their dependence on the magnetic-field intensity, superlattice period, and temperature, is performed. By taking into account the detailed properties of the magnetic subbands, the joint density of states, the transition matrix elements, and the effective sheet concentration of electrons involved in the optical transitions, a simple theoretical explanation is given for some experimental results previously reported.48745164523