  We present 2.4" resolution, high sensitivity radio continuum observations of
the nearby spiral galaxy NGC 4258 in total intensity and linear polarization
obtained with the Very Large Array at 3.6 cm (8.44 GHz). The radio emission
along the northern jet and the center of the galaxy is polarized and allows
investigation of the magnetic field. Assuming energy-equipartition between the
magnetic field and the relativistic particles and distinguishing between (1) a
relativistic electron-proton jet and (2) a relativistic electron-positron jet,
we obtain average magnetic field strengths of about (1) 310\muG and (2) 90\muG.
The rotation measure is determined to range from -400 to -800 rad/m^2 in the
northern jet. Correcting the observed E-vectors of polarized intensity for
Faraday rotation, the magnetic field along the jet turns out to be orientated
mainly along the jet axis. An observed tilt with respect to the jet axis may
indicate also a toroidal magnetic field component or a slightly helical
magnetic field around the northern jet.
