  We describe fully self-consistent N-body experiments of barred galaxies with
massive halos. A rotating bar is braked through dynamical friction with the
halo, which occurs on a short time scale when the central density of the halo
is high. On the other hand, friction is weak in a model with a central halo
density low enough that the disk dominates the rotation curve in the inner
parts; this model supports a fast bar for a Hubble time. We conclude that real
barred galaxies in which the bar rotates rapidly, which is believed to be the
rule, must have close to maximum disks.
