  We present the result obtained from a study, based on long-slit spectroscopy,
of the kinematics and ionization mechanisms of the line-emitting gas for a
sample of four high/intermediate-redshift radio galaxies. In two of the
galaxies (3C352 and 3C435A) the radio sources are of the same scale as the
emission-line regions, whereas in the other two (3C34 and 3C330) the radio
sources are extended on a larger scale than the emission-line structures. We
see evidence for shock-acceleration of the emission-line gas in the extended
regions of all the galaxies, even in the largest radio sources of our sample,
in which the radio hot spots have passed the extended gas of the galaxies. The
extended regions present highly disturbed kinematics (line-splitting and/or
underlying broad components), which are difficult to explain if we do not
consider a strong interaction between the radio-emitting components and the
ambient gas. However, the dominant ionization mechanism of the line-emitting
gas remains uncertain. We have compared the optical diagnostic line ratios of
the galaxies in our sample with both AGN-photoionization and shock-ionization
models. We find a lack of consistency in explaining the main ionization
mechanism of the emission-line gas. This suggest that, if the extended regions
are shock-ionized, some of the assumptions implicit in the shock models may
need to be reconsidered. In addition, we have investigated the nebular
continuum cointribution to the UV excess in the galaxies of our sample. We find
a substantial nebular emission contribution to the UV continuum in all the
cases. However, after the subtraction iof the nebular component, a significant
UV excess remains in the extended nebulae of most of the objects.
