We present the results of a search for X–ray luminous distant clusters of galaxies .
We found extended X–ray emission characteristic of a cluster towards two of our candidate clusters of galaxies .
They both have a luminosity in the ROSAT bandpass of \simeq 10 ^ { 44 } { erg s ^ { -1 } } and a redshift of > 0.5 ; thus making them two of the most distant X–ray clusters ever observed .
Furthermore , we show that both clusters are optically rich and have a known radio source associated with them .
We compare our result with other recent searches for distant X–ray luminous clusters and present a lower limit of 1.2 \times 10 ^ { -7 } { Mpc ^ { -3 } } for the number density of such high redshift clusters .
This limit is consistent with the expected abundance of such clusters in a standard ( b=2 ) Cold Dark Matter Universe .
Finally , our clusters provide important high redshift targets for further study into the origin and evolution of massive clusters of galaxies .