Considerable progress has been made in achieving consensus amongst pathologists and in refining the ISHLT 2005 working formulation criteria for the pathologic diagnosis of AMR (Boxes 1 and 2). Several technical and interpretative issues have been raised. Although some were resolved and a new grading system proposed, further work is required to standardize and validate the consistency and reproducibility of a proposed scoring system for capillary C4d deposition in EMB specimens. Further additional inquiry is needed to address a number of unresolved and essential issues, such as the early histopathologic features of AMR. This can be achieved by establishing a central ISHLT-supported database for collection of digitized images and data of AMR cases to evaluate and clarify areas of uncertainty both in diagnosis and reproducibility. © 2011 International Society for Heart and Lung Transplantation. All rights reserved.