  Observations suggest a slower stellar rotation relative to gas rotation in
the outer part of the Milky Way Galaxy. This difference could be attributed to
an interaction with the interstellar magnetic field. In a simple model, fields
of order 10 micro Gauss are then required, consistently with the observed
values. This coincidence suggests a tool for estimating magnetic fields in
spiral galaxies. A North-South asymmetry in the rotation of gas in the Galaxy
could be of magnetic origin too.
