  We present radio images of two giant quasars from the Molonglo/1Jy sample,
and make a comparative study of giant radio sources selected from the
literature with 3CR radio sources of smaller sizes to investigate the evolution
of giant sources, and test their consistency with the unified scheme. The
luminosity-size diagram shows that the giant sources are less luminous than
smaller-sized sources, consistent with evolutionary scenarios where the giants
have evolved from the smaller sources, losing energy as they expand. For the
giant sources the equipartition magnetic fields are smaller, and
inverse-Compton losses with the microwave background radiation dominates over
synchrotron losses, while the reverse is true for the smaller sources. The
giant radio sources have core strengths similar to those of smaller sources of
similar total luminosity; hence their large sizes are unlikely to be due to
stronger nuclear activity. The radio properties of the giant radio galaxies and
quasars are consistent with the unified scheme.
