Given that most of the vertebrate organs consist of different cell types and that the distribution of modified cytosine bases is tissue and cell-type specific 16-18, 20, 23, 25-27, determining the spatial distribution of oxidized 5mC derivatives in different tissues becomes an important experimental task necessary for unveiling their biological functions. Most of the biochemical and antibody based approaches do not provide any spatial information regarding the distribution of the modified forms of 5mC in different tissue and cell-types. In contrast, immunochemistry based techniques can provide a rapid tool for assessing the spatial distribution and nuclear localization of 5mC28 and its oxidized derivatives20. That is said, the reported very low abundance of 5fC (20 in every 106 cytosine) and 5caC (3 in every 106 cytosine) in the mouse genome18 represents a significant challenge for standard immunochemistry.