During the last decade and since its initial discovery in 1998, the application of the γH2AX methodology has provided a significant boost towards reliable measurements of DSBs at a cellular or tissue level . On the other hand, for the measurement of non-DSB lesions at least in situ, significant advancements have been made using adaptations of fluorescence microscopy and foci colocalization as reviewed in , but still there is no reliable in situ-technique to detect closely spaced DNA lesions within 1–20 bp apart. The colocalization of two or more antibodies (corresponding to DNA repair proteins presumably working on a clustered damage site), certainly provides valuable information, but this only gives an idea on how many different proteins maybe present in a chromosome region of a few Mbp. In each case, measurement of DNA lesions is being performed indirectly by the use of usually two DNA damage/repair proteins specific primary antibodies (e.g., against γ-H2AX:DSB and OGG1:oxidized purines or NTH1:oxidized pyrimidines etc.) each detected by the appropriate fluorescent labeled secondary antibodies. The simultaneous use of more than three different antibodies requires highly advanced microscopic systems and it is considered to be highly challenging. This microscopy-based methodology however, is very distant from the original definition of clustered DNA damage located in a very small DNA region . Based on the above and in an attempt to make a rough comparison between the originally used adaptations of gel electrophoresis to measure different types of DNA clusters (DSBs and non-DSBs) as introduced by Sutherland and colleagues  and afterwards by others  one can conclude that: (1) there are two main methodologies to measure complex DNA lesions at the cellular level; one based on DNA fragmentation measurement using gel electrophoresis with repair enzymes as damage probes, and in situ immunofluorescence microscopic approaches using different antibodies to allow foci colocalization centered around the DSB focus (usually γH2AX/53BP1) (Figure 1 and Figure 2) both methodologies are necessary and useful, but they are complementary; when it comes to measurement of damage complexity of DSBs and non-DSBs one should consider applying them both. A short description on the powerful γH2AX methodology follows.