  We reconsider the rejuvenation mechanism as proposed by Shull, Fesen, & Saken
(1989). These authors suggest that an active pulsar can catch up with, and
rejuvenate the shell of the associated supernova remnant. The morphology of the
SNRs G5.4-1.2 and CTB80 seem to confirm this rejuvenation mechanism. The
spindown energy is deposited by the pulsar as a relativistic pulsar wind, and
has a sufficient power to explain the observed radio emission observed in these
remnants. Shull et al. (1989) did {\it not} explain the observed lengthscales
of the rejuvenated parts of the SNR shell. therefore one needs to consider the
diffusive transport of the injected electrons by the pulsar wind. We propose to
apply a diffusion mechanism as introduced by Jokipii (1987), which makes a
distinction between diffusion along the magnetic field lines and perpendicular
to the magnetic field lines, parameterised by the gyro factor $\eta$. We show
that one has to assume a high value for the gyro factor, $\eta\simeq
10^3-10^4$, i.e. diffusion of the electrons along the magnetic field line is
much faster then perpendicular to the magnetic field line, in order for the
rejuvenation mechanism to work on the observed lengthscales.
