This document discusses a Z39.50 Interoperability Testing framework. In a first phase of the Z39.50 Interoperability Testbed, a large dataset of MARC records was used. In this work, the authors are exploring how a set of special, diagnostic MARC records can be developed and used to identify interoperability problems between a Z39.50 client and a Z39.50 server providing access to a database of bibliographic records supporting the search and retrieval functions of an online library catalog. The authors refer to these special, diagnostic records as radioactive MARC records. It discusses the various components and identifies the tasks related to developing and implementing the components.