In order to interpret the ‘irreversibility line’ found in most found in most high‐Tcsuperconductors, it is necessary to understand how pinning modifies the flux lattice melting transition. Here, the effect of pinning is incorporated in a quasi‐two‐dimensional formulation, which should be appropriate for these highly anisotropic materials. Comparing the results to experiment, it is found that the flux lattice appears to be very different in YBa2Cu3O7−&dgr;than in the Bi‐ and Tl‐layered materials.