A Hartree approximation is used to study the interplay of two kinds of
scaling which arise in high-temperature superconductors, namely criti
cal-point scaling and that due to the confinement of electron pairs to
their lowest Landau level in the presence of an applied magnetic fiel
d. In the neighborhood of the zero-field critical point, thermodynamic
functions scale with the scaling variable [T - T(c2)(B)]/B1/2nu, whic
h differs from the variable [T - T(c)(0)]/B1/2nu suggested by the Gaus
sian approximation. Lowest-Landau-level (LLL) scaling occurs in a regi
on of high field surrounding the upper critical-field line but not in
the vicinity of the zero-field transition. For YBa2Cu3O7-delta in part
icular, a field of at least 10 T is needed to observe LLL scaling. The
se results are consistent with a range of recent experimental measurem
ents of the magnetization, transport properties, and, especially, the
specific heat of high-T(c) materials.