  We extract groups of galaxies from the SDSS Data Release 5 with the purpose
of studying the supercluster-void network and environmental properties of
groups therein. We use a modified friends-of-friends (FoF) method with adopted
variable linking length in transverse and radial direction to eliminate
selection effects and to find reliably as many groups as possible to track the
supercluster network. We take into account various selection effects due to the
use of a magnitude limited sample. To determine linking length scaling we study
the luminosity-density relation in observed groups. We follow the changes in
group sizes and mean galaxy number densities within groups when shifting nearby
groups to larger distances. As a result we show that the linking length should
be a slowly growing function with distance. Our final sample contains 17143
groups in the equatorial, and 33219 groups in the northern part of the DR5
survey with membership N_g >= 2. The group catalogue is available at our
web-site http://www.obs.ee/~erik/index.html.
  Due to a narrow magnitude window in the SDSS the group catalogue based on
this survey has been obtained by moderately growing linking length scaling law
up to redshift z = 0.12. Above this redshift the scaling law turns down. In the
redshift range z=0.12 - 0.2 only the cores are detected. Along with applying
weights when calculating luminosities it is possible to use groups for
determination of the large-scale luminosity-density field.
