Photometry in [OIII] emission of Planetary Nebulae in external galaxies can be used to determine distances as great as that of the Virgo cluster and beyond, as forcefully argued elsewhere during this conference (G.H. Jacoby, invited talk). In addition, measurement of the radial velocities of the PN allows dynamical behaviour to be probed to much greater distance from the galaxian centre than integrated light techniques (e.g. Arnaboldi 1994).