High Redshift X-ray Clusters and ${\Omega_{0}}$
  X-ray clusters are powerful tools for the determination of cosmological parameters. More specifically, the combined knowledge of the redshift distribution of X-ray clusters together with the luminosity-temperature correlation, $L_X-T_X$ provides us a new test for constraining the mean density of the universe ${\Omega_{0}}$. After a brief description of this test, I will present the result of our first attempt to apply this test to current X-ray data. 
R. Sadat