Sodium vapour is excited by D 2 radiation. The linear polarization of the fluorescent D 2 radiation emitted at right angles to the incident-light beam is measured as a function of the pressure of an added noble gas. A magnetic field of 270 Oe which points parallel to the incident-light beam, serves to decouple the nuclear spin in the excited state. From the decrease of the polarization observed at rising pressure, cross sections for the disalignment of the electron in the excited state are derived. They are 167, 174, 308, 341, 376 Å 2 for the noble gases He, Ne, Ar, Kr, Xe at 383 K. These and earlier results on sodium depolarization are summarized and compared with theoretical results by Masnou et al., Reid, and Lewis et al. Satisfactory agreement is obtained.