  We report optical spectroscopic observations of a sample of 6 low-galactic
latitude microquasar candidates selected by cross-identification of X-ray and
radio point source catalogs for |b|<5 degrees. Two objects resulted to be of
clear extragalactic origin, as an obvious cosmologic redshift has been measured
from their emission lines. For the rest, none exhibits a clear stellar-like
spectrum as would be expected for genuine Galactic microquasars. Their
featureless spectra are consistent with being extragalactic in origin although
two of them could be also highly reddened stars. The apparent non-confirmation
of our candidates suggests that the population of persistent microquasar
systems in the Galaxy is more rare than previously believed. If none of them is
galactic, the upper limit to the space density of new Cygnus X-3-like
microquasars within 15 kpc would be 1.1\times10^{-12} per cubic pc. A similar
upper limit for new LS 5039-like systems within 4 kpc is estimated to be
5.6\times10^{-11} per cubic pc.
