  A project which aims to understand the abundance patterns of He, C, N, O, Ne,
S, and Ar for a small sample of planetary nebulae is described. Abundance
ratios of O/H, C/O, and N/O especially show a broad range relative to their
solar values, and AGB stellar evolution models used to interpret the patterns
indicate that reasonable ranges in progenitor mass and metallicity are adequate
to explain the observed abundance spread. Chemical yields of intermediate-mass
stars inferred from these same models are used to calculate chemical evolution
models of the solar neighborhood. These models indicate that intermediate-mass
stars account for roughly half of the C-12 and nearly all of the N-14 in that
region.
