  (Abridged:) The paradox of apparent optical associations of galaxies with
very different redshifts, the so-called anomalous redshift problem, is around
35 years old, but is still without a clear solution and is surprisingly ignored
by most of the astronomical community. Statistical correlations among the
positions of these galaxies have been pointed out by several authors.
Gravitational lensing by dark matter has been proposed as the cause of these
correlations, although this seems to be insufficient to explain them and does
not work at all for correlations with the brightest and nearest galaxies. Some
of these cases may be just fortuitous associations in which background objects
are close in the sky to a foreground galaxy, although the statistical mean
correlations remain to be explained and some lone objects have very small
probabilities of being a projection of background objects.
  The sample of discordant redshift associations given in Arp's atlas is indeed
quite large, and most of the objects remain to be analysed thoroughly. For
about 5 years, we have been running a project to observe some of these cases in
detail, and some new anomalies have been added to those already known; For
instance, in some exotic configurations such as NGC 7603 or NEQ3, which can
even show bridges connecting four object with very different redshifts. Not
only QSOs but also emission-line galaxies in general are found to take part in
this kind of event. Other cases are analyzed: MCG 7-25-46, GC 0248+430, B2
1637+29, VV172 and Stephan's Quintet.
