  Many observations of late-type M stars show large near-spherical
circumstellar envelopes, yet planetary nebulae and supernova remnants are
frequently axisymmetric. We present VLBI and MERLIN observations of masers
around the red supergiant S Per which show varying degrees of axisymmetry and a
dynamically significant magnetic field. There is no evidence for rotation here
or in most similar objects. We examine possible origins of the magnetic field.
