[en] In a very interesting paper, Tremaine and Gunn have claimed that light neutral leptons of mass approximately <1 MeV/c² cannot play a significant role in the astrophysics of galaxies and in cosmology. Here, we point out some oversights in their argument. When these oversights are corrected, we find that no really serious limits on neutrino masses can be derived from astrophysical arguments, and can only come from the cosmological consideration that we know the total mass in the Universe to be not much above the critical mass required to have a closed Universe. (author)