  We analyze the density profiles and virial radii for a sample of 90 nearby
clusters, using galaxies with available redshifts and positions. Each cluster
has at least 20 redshifts measured within an Abell radius, and all the results
come from galaxy sets of at least 20 members. Most of the density profiles of
our clusters are well fitted by hydrostatic-isothermal-like profiles. The
slopes we find for many cluster density profiles are consistent with the
hypothesis that the galaxies are in equilibrium with the binding cluster
potential. The virial radii correlate with the core radii at a very high
significance level. The observed relationship between the two size estimates is
in agreement with the theoretical one computed by using the median values of
the density profile parameters fitted on our clusters. After correcting for
incompleteness in our cluster sample, we provide the universal distributions
functions of core and virial radii (obtained within half an Abell radius).
