  We present results from an ongoing survey of infrared emission lines from the
neutron-capture elements Se and Kr in Galactic planetary nebulae (PNe). Se and
Kr may be produced in the initial steps of the s-process during the asymptotic
giant branch (AGB) phase of PN progenitor stars, and brought to the surface by
convective dredge-up before PN ejection. Therefore, enriched Se and Kr
abundances in PNe indicate that the s-process and dredge-up were active within
the progenitor stars. We have detected the emission lines [Kr III] 2.199 and
[Se IV] 2.287 microns in 68 of 119 Galactic PNe, and used these line fluxes to
derive ionic and total elemental abundances. Using the ionization correction
factors Se^{3+}/Se = Ar^{++}/Ar and Kr^{++}/Kr = S^{++}/S, we find a range of
Se and Kr abundances, from nearly solar to enriched by a factor of 5-10 times,
which implies varying degrees of dredge-up efficiency in the progenitor stars.
We have searched for correlations between n-capture element abundances and
other nebular properties, and find that PNe with Wolf-Rayet central stars tend
to exhibit more elevated Se and Kr abundances than other nebulae. Bipolar
nebulae, believed to arise from the most massive of PN progenitors, may have
lower n-capture abundances than elliptical PNe.
