  The Planetary Nebula Spectrograph is a dedicated instrument for measuring
radial velocity of individual Planetary Nebulae (PNe) in galaxies. This new
instrument is providing crucial data with which to probe the structure of dark
halos in the outskirts of elliptical galaxies in particular, which are
traditionally lacking of easy interpretable kinematical tracers at large
distance from the center. Preliminary results on a sample of intermediate
luminosity galaxies have shown little dark matter within 5 ~ R_eff implying
halos either not as massive or not as centrally concentrated as CDM predicts
(Romanowsky et al. 2003). We briefly discuss whether this is consistent with a
systematic trend of the dark matter content with the luminosity as observed in
an extended sample of early-type galaxies.
