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 the literature and found that they lie at z2.50. Based on the new high quality spectra, we found that only half of the observed objects can be classified as bona-fide BL Lacs.
Cone search capability for table J/ApJ/861/130/bllac (The high redshift SDSS BLLac candidates with their observation log obtained at the Gran Telescopio CANARIAS (GTC) and the properties of the optical spectra (tables 1-3))