  A dynamical model for correlated two-pion and two-kaon exchange in the
baryon- baryon interaction is presented, both in the scalar-isoscalar
($\sigma$) and the vector-isovector ($\rho$) channel. The correlations between
the two pseudoscalar mesons are taken into account by means of $\pi\pi - K\bar
K$ amplitudes derived from a meson-exchange model, which is in line with the
empirical $\pi\pi$ data. It is found that correlated $K\bar K$ exchange plays
an important role in the $\sigma$-channel for baryon-baryon states with non-
vanishing strangeness. The strength of correlated $\pi\pi$ plus $K\bar K$
exchange in the $\sigma$-channel decreases with the strangeness of the baryon-
baryon system becoming more negative. The results for correlated $\pi\pi$-
exchange in the vector-isovector channel deviate from what is expected in the
naive SU(3) picture for genuine $\rho$-exchange. Shortcomings of a simplified
description in terms of sharp mass $\sigma$- and $\rho$-exchange are pointed
out.
