Tyrosyl-DNA phosphodiesterase-2 (TDP2) functions to remove trapped topoisomerase II/DNA complexes by processing 5′- blocking protein (topo II) at the site of the DNA break (Fig 1). Assaying this activity can be difficult, requiring labeled oligos and isotopes or complicated detections that are hard to set up. In many cases, these assays are largely derivative from the actual reaction using the natural substrate (Fig. 1). We have developed a very simple substrate that makes it easy to assay Tdp2. This substrate is a kDNA/Top2 covalent complex (Fig. 2, see red arrow). Following Tdp2 reaction, a linear kDNA product is released, which can easily be detected in a 1% agarose gel.