The irreversibility line for a high quality melt-textured YBa2Cu3O7-δ sample was determined in two orientations of the field H relative to the sample c axis. In both orientations we obtain good fits using a melting equation with quantum correction to describe the Abrikosov-lattice melting. The angular-scaling rule for uniaxially anisotropic materials is verified, giving additional support for the melting hypothesis. Our results are similar to those found in the literature for very clean untwinned samples. We suggest that the Abrikosov-lattice melting is weakly affected by quenched disorder, at least in the relatively low fields (H≤50 kOe) and high temperatures (T/Tc>0.8) probed in this work. © 1995 The American Physical Society.511493839386