  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.
