  Studies of limits on active-sterile neutrino mixing derived from big bang
nucleosynthesis considerations are extended to consider the dependance of these
constraints on the primordial deuterium abundance. This study is motivated by
recent measurements of D/H in quasar absorption systems, which at present yield
discordant results. Limits on active-sterile mixing are somewhat relaxed for
high D/H. For low D/H ($\approx 2 \times 10^{-5}$), no active-sterile neutrino
mixing is allowed by currently popular upper limits on the primordial $^4$He
abundance $Y$. For such low primordial D/H values, the observational inference
of active-sterile neutrino mixing by upcoming solar neutrino experiments would
imply that $Y$ has been systematically underestimated, unless there is new
physics not included in standard BBN.
