  Recent determinations of the upper mass limit to the local initial mass
function (IMF) claim a value of m(upper)=50+/-10 solar masses, based upon
direct comparisons of the observed oxygen and iron abundances in metal-poor
stars with the predicted stellar yields from Type II supernovae (SNe). An
unappreciated uncertainty in these analyses is the input physics intrinsic to
each SNe grid, and its effect upon stellar nucleosynthesis. We demonstrate how
such uncertainties, coupled with the uncertain metal-poor halo star
normalization, while allowing us to set a lower bound to m(upper) of
approximately 40 solar masses, nullifies any attempt at constraining the upper
bound.
