Aims:We aim to identify the nature of several objects previously catalogued as ultra-luminous X-ray (ULX) source candidates. Methods: Long-slit spectroscopy of the optical counterparts has been carried out. Results: The eight objects are at higher redshift than their putative parent galaxies. Conclusions: It is found that these eight previously catalogued ULX candidates, most of them projected in galactic halos are actually background unrelated objects. This result confirms the high degree of contamination present in current catalogues of ULXs.