Spectrophotometric data, including [O II] 3726, 3729 Å doublet ratios, are presented for 32 planetary nebulae (PN) in the Magellanic Clouds. It is argued that the electron densities derived from these ratios provide a much better diagnostic for the determination of nebular masses than previously assumed. The 32 PN are classified as either Type I or else as optically thick or optically thin in the hydrogen Lyman continuum. The optically thick PN are found to all have electron densities greater than 6000 cm –3 , while the optically thin PN all have electron densities below 5000 cm –3. The optically thin PN show a range of only a factor of 2.0 in their derived masses, and have a mean ionized mass of 0.27±0.06M⊙. The absolute Hβ fluxes of the optically thick nebulae show a range of only a factor of 1.8. The application of these results to Galactic PN would yield distances which are generally larger than those previously estimated. A method of distance determination is proposed for optically thin PN that uses integrated nebular [O II] electron densities rather than angular diameters
