2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46327A computation of nucleosynthesis bounds on the masses of long-lived Dirac and Majorana neutrinos is reviewed. In particular an explicit treatment of the ``differential heating'' of the $\nue$ and $\bnue$ ensembles due to the residual out-of-equilibrium annihilations of decoupled heavy neutrinos is included. The effect is found to be considerably weaker than recently reported by Dolgov et al. For example, the bounds for a Dirac tau neutrino are $\mnt < 0.37$ MeV or $\mnt > 25$ MeV (for $\dNu > 1$), whereas the present laboratory bound is $\mnt < 23.1$ MeV.6 pages, 2 eps-figures. Talk at Neutrino 96High Energy Physics - PhenomenologyAstrophysicstext