  The issue of the observability of Old Isolated Neutron Stars (ONSs) accreting
from the interstellar gas, is reconsidered using the spectra presented in
Zampieri {\it et al.\/} (1995). In particular, we focus our attention on the
overall soft X--ray emission of ONSs, which may provide a substantial
contribution to the X--ray background in the 0.5--2 keV band. It is found that
if accretion is channeled into polar caps by a magnetic field of $\sim 10^9$ G,
up to $\sim$ $12-25 \%$ of the unresolved soft excess observed at high
latitudes in the X--ray background can be explained in terms of emission from
accreting isolated ONSs. However, this would imply the detection with ROSAT of
$\sim 10$ sources deg$^{-2}$ above a threshold of $\sim 10^{-14} \, {\rm erg\,
cm^{-2} s^{-1}}$. A brief reconsideration of the observability of isolated ONSs
as individual X--ray sources is also presented.
