  If the gravitino is sufficiently light and stable it will behave as an
effective massless neutrino species at the time of nucleosynthesis. Depending
on the temperature at which it decouples from the thermal bath in the early
universe, the gravitino mass will be bounded by the primordial $^4$He
abundance. Assuming a conservative estimate that the number of neutrino
families, $N_\nu < 3.6$, superlight gravitinos with a mass $m_{3/2} \lesssim
10^{-6}$eV are ruled out. This bound is weaker than previous estimates because
the Goldstino annihilation cross section was overestimated.
