Many extended radio sources seem to need in situ regeneration of the relativistic electrons. MHD turbulence generated by surface instabilities has been suggested as the reacceleration mechanism. However, Eilek (1981) has shown that short wavelength MHD waves, which are the most effective particle accelerators, are strongly damped in radio sources. This results in the turbulent region being confined to a thin layer on the edge of the source, so that particles accelerated here must propagate into the radio source if this reacceleration mechanism is to account for the internal synchrotron luminosity. Most likely the particles diffuse across tangled field lines; using numerical modelling of the turbulence, Eilek showed that the particles propagate only a small distance (10 pc–1 kpc) in from the edge. This predicts that larger sources should appear limb brightened; but such limb brightening is rare. If short wavelength MHD waves are indeed the source of reacceleration, they must be generated internally.