  Concern about systematic uncertainty in the $^4$He abundance as well as the
chemical evolution of $^3$He leads us to re-examine this important limit. It is
shown that with conservative assumptions no more than the equivalent of 4
massless neutrino species are allowed. Even with the most extreme estimates of
the astrophysical uncertainties a meaningful limit still exists, less than 5
massless neutrino species, and illustrates the robustness of this argument. A
definitive measurement of the deuterium abundance in high-redshift hydrogen
clouds should soon sharpen the limit.
