Topoisomerases can release topological stress and resolve DNA catenanes by a DNA strand breakage and re-ligation mechanism. During the lifetime of the DNA break, the topoisomerase remains covalently linked to the DNA and removes itself when the break is re-ligated. While the lifetime of a covalent topoisomerase-DNA complex is usually short, several clinically important cancer drugs kill cancer cells by inhibiting the removal of covalently linked topoisomerases. The topoisomerase-like protein Spo11 is responsible for meiotic double strand break formation. Spo11 is not able to remove itself and is removed by nucleolytic cleavage. This chapter describes a method which allows the reproducible and quantitative detection of proteins covalently bound to the DNA