  During the start of a survey program using FORS2 long slit spectroscopy on
planetary nebulae (PN) and their haloes, we serendipitously discovered six
background emission line galaxies (ELG) with redshifts of z = 0.2057, 0.3137,
0.37281, 0.4939, 0.7424 and 0.8668. Thus they clearly do not belong to a common
cluster structure. We derived the major physical properties of the targets.
Since the used long slit covers a sky area of only 570 arcsec^2, we discuss
further potential of serendipitous discoveries in archival data, beside the
deep systematic work of the ongoing and upcoming big surveys. We conclude that
archival data provide a decent potential for extending the overall data on ELGs
without any selection bias.
