  It has recently been suggested that cosmologically significant numbers of
black holes could form during a first-order QCD phase transition. Further, it
has been asserted that these black holes would have masses corresponding
naturally to the inferred mass ($\sim 1 M_{\odot}$) of the MACHOs responsible
for the observed gravitational microlensing events. In this model, the
underlying spectrum of primordial density perturbations provides the
fluctuations that give rise to black holes at the epoch of the QCD transition.
We employ a simplified model to estimate the reduction in the critical
overdensity of a horizon-sized primordial perturbation required for collapse to
a black hole. We find that a first-order QCD transition does indeed produce a
sharp peak in the black hole mass spectrum, but that this peak corresponds to
the horizon mass at an epoch somewhat earlier than the cosmological transition
itself. Assuming a COBE normalized primordial density perturbation spectrum
with constant spectral index, for the black holes so produced to be
cosmologically significant would require an extremely finely tuned ``blue''
primordial density perturbation spectrum. Specifically, in the context of our
simplified model, a spectral index in the range $n=1.37-1.42$ corresponds to
the range $\Omega \sim 10^{-5}-10^3$ of the black hole contribution to the
present-day density parameter.
