  The three dimensional uniformly frustrated XY model is used as a model of a
high temperature superconductor in an applied magnetic field parallel to the
CuO-planes. Through Monte Carlo simulations with anisotropy $\eta^2 = 10$ on
large lattices we find evidence for a first order transition. Earlier
simulations and theoretical treatments are discussed and the experimentally
found smooth onset of resistivity is suggested to be due to a large potential
barrier against vortex line motion above $T_c$ present for perfect alignment of
the applied field.
