  We evaluate, within one-loop chiral perturbation theory, the two-pion
exchange diagrams with single and double delta-isobar excitation contributing
to elastic NN-scattering. We find that virtual $\Delta$-excitation processes
(in the static limit) produce the correct amount of isoscalar central
attraction as needed in the peripheral partial waves with $L\geq 3$.
Furthermore we compute the two-loop diagrams involving the $\pi\pi$-interaction
(so-called correlated $2\pi$-exchange). Contrary to common believe these
processes lead to negligibly small and repulsive corrections to the
NN-potential. The exchange of vector mesons ($\rho, \omega$) turns out to be
important for the F-wave phase shifts above $T_{lab}=150$ MeV. Without
adjustable parameters we are able to reproduce the empirical NN phase shifts up
to 350 MeV for $L\geq 3$ and up to about (50--80) MeV for the D-waves. This is
therefore the characteristic window in which the NN-interaction is basically
governed by chiral symmetry. Not surprisingly, the lower partial waves require
non-perturbative methods and additional short-distance parametrizations of the
NN-dynamics.
