  The contribution from hyperons to the bulk viscosity of neutron star matter
is calculated. Compared to previous works we use for the weak interaction the
one-pion exchange model rather than a current-current interaction, and include
the neutral current $nn \leftrightarrow n\Lambda$ process. Also the sensitivity
to details of the equation of state is examined. Compared to previous works we
find that the contribution from hyperons to the bulk viscosity is about two
orders of magnitude smaller.
