SIMBAD references

We present results of first epoch high resolution imaging observations of four extremely distant quasars. The sample includes the only two radio-loud quasars at redshift z>4 known to the date of observations, 1251-407 (z=4.46) and 1508+572 (z=4.30). The 5 GHz observations of 1251-407, 1351-018 (z=3.71) and 1354-174 (z=3.15) were made with the VLBA in January 1995. The source 1508+572 was observed with the EVN in May 1995. The milliarcsecond scale structures of these quasars are dominated by compact cores. The two z>4 quasars are unresolved on the baselines observed. We show that the apparently less prominent milliarcsecond scale extended radio structures in high redshift quasars than in their low redshift counterparts may be explained by the difference in spectral indices of the cores and jets.