  We have obtained isofield curves for the square root of the average kinetic
energy density of the superconducting state for three single crystals of
underdoped YBa_2Cu_3O_{7-x}, an optimally doped single crystal of
Bi_2Sr_2CaCu_2O_{8+\delta}, and Nb. These curves, determined from isofield
magnetization versus temperature measurements and the virial theorem of
superconductivity, probe the order parameter amplitude near the upper critical
field. The striking differences between the Nb and the high-T_c curves clearly
indicate for the latter cases the presence of a unique superconducting
condensate below and above T_c.
