Dredge-up effects in galactic and magellanic planetary nebulae

Chemical abundances are reported for 23 planetary nebulae in the Small Mage llanic Cloud. Average abundances agree with values found for HII regions, s uggesting that progenitors of most of these objects have been formed in the last 1 - 2 Gyr. The N/O vs. O/H anticorrelation is confirmed for Magellani c and galactic planetaries, and a more robust. result is obtained if object s of similar ages (or masses) are grouped together. For a given class, such a negative correlation suggests that the surface enrichment due to dredge- up episodes is more efficient at lower metallicities, in agreement with rec ent computations.