  We report on 16 BL Lacertae objects that were proposed to be at z > 1. We
present spectroscopic observations secured at the 10.4m GTC that allowed us to
assess the redshift of these sources. In particular, for five objects we
disprove the previous value of the redshift reported in literature and found
that they lie at z < 1. Moreover, two of them exhibit broad emission lines that
are not characteristic of BL Lacertae object. On the other hand, for eight
targets we improve the tentative value of z, previously based on only one
feature, by detecting a number emission lines. Finally, in three cases we
detect onset of Ly-{\alpha} forest at z > 2.50. Based on the new high quality
spectra we found that only half of the observed objects can be classified as
bona-fine BL Lacs.
