  The presence of gas in dusty debris disks around main-sequence stars is
reviewed. We present new observational results for the most prominent
representative of the class, viz. the southern naked-eye star beta Pictoris.
The spatial and spectral distribution of observed atomic lines from the disk
around the star is reproducable by a Keplerian rotation model to a high degree
of accuracy. The expected velocity dispersion due to radiation pressure in
resonance lines is not observed. Modeling the motion of different atomic
species under the influence of gravity, radiation pressure and gas friction
leads to the conclusion that an underlying decelerating component must be
present in the disk. This braking agent is most likely hydrogen, with inferred
average densities n(H) > 1e6 per cubic centimeter. This could support the
observational result of Thi et al. (2001) which indicated the presence of
appreciable amounts of H2 around the star beta Pic.
