  Observational determinations of the correlation between the characteristic
density delta_c and the virial mass M_vir of dark halos constitute a critical
test for models of hierarchical structure formation. Using the dynamical
properties of dark halos reconstructed from the galaxy distributions in massive
systems (groups/clusters) and the rotation curves in less massive systems
(dwarf, low surface brightness and spiral galaxies) drawn from the literature,
we confirm the existence of the delta_c-M_vir relation over a broad mass range
from 10**10 to 10**15 solar masses, which is in gross consistency with the
prediction of a flat cosmological model with Omega_M=0.3 and Omega_Lambda=0.7.
It is pointed out that previous analyses based on the measurements of X-ray
emitting gas and the hydrostatic equilibrium hypothesis, which claimed a
shallower scale-free spectrum of n=-1 for initial density fluctuations, may
suffer from nongravitational heating influence especially in low-mass systems.
