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 ^ { II } | \leq 5 \degr .
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 \la 1.1 \times 10 ^ { -12 } pc ^ { -3 } .
A similar upper limit for new LS~5039 -like systems within 4 kpc is estimated to be \la 5.6 \times 10 ^ { -11 } pc ^ { -3 } .