  Using the Ginzburg-Landau theory in very general terms, we develop a simple
scaling procedure which allows to establish the temperature dependence of the
upper critical field and the value of the superconducting critical temperature
Tc of type-II superconductors from measurements of the reversible isothermal
magnetization. An analysis of existing experimental data shows that the
normalized dependencies the upper critical field on T/Tc are practically
identical for all families of high temperature superconductors at all
temperatures for which the magnetization data are available.
