[en] The influence of a magnetic field on the thermal conductivity of high-T_c superconductors is described. A semi-phenomenological model which takes into account the influence of the magnetic field on the density of normal electrons as well as on the electron-vortex scattering is used, assuming that the energy levels of quasiparticles near the vortex cores are quantized and supposing that electrons are mainly scattered by these quasiparticles. The experimental results on an untwinned YBa₂Cu₃O_7-δ single crystal, on YBa₂Cu₃O_7-δ and YBa₂(Cu_0.95Fe_0.05)₃O_7-δ ceramics are quite well reproduced with quite realistic values of the physical parameters. (author). Letter-to-the-editor