  We calculate in baryon chiral perturbation theory the relativistic
$1/M^2$-corrections to the leading order two-pion exchange diagrams. We give
explicit expressions for the corresponding one-loop NN-amplitudes in momentum
space. The resulting isovector central and isoscalar spin-spin and tensor
NN-amplitudes involve non-static terms proportional to the squared nucleon
center-of-mass momentum $p^2$. From the two-pion exchange box diagrams we
obtain an isoscalar quadratic spin-orbit NN-amplitude. We give also analytical
expressions for the corresponding NN-potentials in coordinate space. The
diagrammatic results presented here make the chiral NN-potential complete at
next-to-next-to-next-to-leading order.
