  We found that in regions of high mass star formation the CS emission
correlates well with the dust continuum emission and is therefore a good tracer
of the total mass while the N$_2$H$^+$ distribution is frequently very
different. This is opposite to their typical behavior in low-mass cores where
freeze-out plays a crucial role in the chemistry. The behavior of other high
density tracers varies from source to source but most of them are closer to CS.
Radial density profiles in massive cores are fitted by power laws with indices
about -1.6, as derived from the dust continuum emission. The radial temperature
dependence on intermediate scales is close to the theoretically expected one
for a centrally heated optically thin cloud. The velocity dispersion either
remains constant or decreases from the core center to the edge. Several cores
including those without known embedded IR sources show signs of infall motions.
They can represent the earliest phases of massive protostars. There are
implicit arguments in favor of small-scale clumpiness in the cores.
