GTG-banded slides are often considered unusable for further molecular cytogenetic analyses. In this chapter, we describe a simple protocol for reactivating such GTG-banded slides for further use in molecular cytogenetics. The slides may have been embedded with Eukitt® or “Canada-balsam” or may not have been covered with a cover slip at all. This option allows archive material from rare cytogenetic aberrations to be examined and more in-depth investigations to be carried out on actual cases with limited access to material.