The planetary nebula luminosity function for the bulge of M31 (black points with error bars). These data, which extend over nearly 5 mag, represent the deepest M31 PNLF currently available. The solid line shows the model PNLF (an exponential with a bright-end cutoff) that was adopted by Ciardullo et al. (1989). The magnitudes of the clusters PNe are marked: Milky Way PNe on the lower row, and M31 PNe on the upper row. The red circles, blue triangles, and tan squares represent PN candidates in old confirmed clusters, young clusters, and candidate globular clusters, respectively.