Until now, [O III] λ5007 surveys of extragalactic planetary nebulae (PN) have been aimed at determining distances and identifying test particles for future (cinematica] studies. However, PN observations are useful in another area of astrophysics - the investigation of stellar populations. Because the production rate of [O III] bright PN in a galaxy can vary by an order of magnitude, this number is potentially a powerful discriminant between age and metallicity in an evolved stellar population. A strong inverse correlation exists between galaxy absolute magnitude and bolometric luminosity-specific PN density (α2.5), with the small metal-poor ellipticals having values of α2.5 in exact accordance with the predictions of stellar evolution theory. This correlation, along with the direct dependence of α2.5 on galactocentric radius, and the scatter in α2.5 seen in “young” galaxies, argues strongly that elliptical galaxies are old systems which follow a metallicity sequence. It also suggests that the combination of absorption line spectroscopy, UV photometry, and PN measurements can be a powerful probe of elliptical galaxy stellar populations.