Optical spectroscopy of three recently discovered BL Lacs (PG 1246+586, PG 1424+240 and PG 1437+398) in the Palomar-Green optical survey is presented. The three sources have featureless spectra and the continuum is well represented by a power law model with slopes typical of BL Lac objects. The observations together with data at other frequencies collected from the literature, are used to construct the overall energy distribution from radio to X-ray and compared with that of all other BL Lac in the PG survey. The overall properties of the small sample of PG BL Lacs objects are shortly discussed.