The MRC/1Jy sample of 559 radio sources with S408 MHz ≥ 0.95 Jy (McCarthy et al. 1996; Kapahi et al. in preparation) is a factor of 5 to 6 times deeper than the 3CRR sample; it is therefore, well suited for disentangling the redshift (z) and luminosity (P) dependence of several properties of extragalaxtic radio sources. Here we present results on the spectral index — redshift correlation for radio galaxies, based on a comparison of the well documented radio spectra (in the rest frame frequency range of about 1 to 16 GHz) of the following two matched-luminosity samples, (a) 14 high redshift radio galaxies (HRRG) from MRC with 2.0 < z < 3.2 and linear size i > 10 kpc, and (b) 21 intermediate z radio galaxies (IRRG) from 3CRR with 0.85 < z < 1.7 and l > 10 kpc. Both samples have P1.4 GHz in the range 1028 and 1028.8 WHz−1.