  We present multi-frequency VLA observations of two giant quasars, 0437-244
and 1025-229, from the Molonglo Complete Sample. These sources have
well-defined FRII radio structure, possible one-sided jets, no significant
depolarization between 1365 and 4935 MHz and low rotation measure ($\mid RM
\mid < 20 rad/m^2$). The giant sources are defined to be those whose overall
projected size is $\geq$ 1 Mpc. We have compiled a sample of about 50 known
giant radio sources from the literature, and have compared some of their
properties with a complete sample of 3CR radio sources of smaller sizes to
investigate the evolution of giant sources, and test their consistency with the
unified scheme for radio galaxies and quasars. We find an inverse correlation
between the degree of core prominence and total radio luminosity, and show that
the giant radio sources have similar core strengths to the smaller sources of
similar total luminosity. Hence their large sizes are unlikely to be due to
stronger nuclear activity. The degree of collinearity of the giant sources is
also similar to the sample of smaller sources. The luminosity-size diagram
shows that the giant sources are less luminous than our sample of smaller-sized
3CR sources, consistent with evolutionary scenarios where the giants have
evolved from the smaller sources losing energy as they expand to these large
dimensions. For the smaller sources, radiative losses due to synchrotron
radiation is more significant while for the giant sources the equipartition
magnetic fields are smaller and inverse Compton losses with the microwave
background radiation is the dominant process. The radio properties of the giant
radio galaxies and quasars are consistent with the unified scheme.
