**3. Conclusion**

The comet assay has proved to be remarkably versatile. Far from being just another way of measuring DNA breaks, it can give quantitative information about base damage if lesionspecific endonucleases are included in the protocol, and by extension it can be used to monitor the cellular repair of such damage (the challenge assay). The NER pathway for helix distortions and bulky adducts can be blocked at the repair synthesis stage by DNA polymerase inhibitors, and this leads to an accumulation of SBs – readily measured with the comet assay. A more biochemical approach to DNA repair is exemplified by the *in vitro* repair assay, in which a cell extract is incubated with a specifically damaged DNA substrate – again leading to an accumulation of DNA breaks – repair intermediates, for which the comet assay is ideally suited as a detector. These different approaches have found application in cell culture studies (e.g. investigating inhibitors and enhancers of repair, and repair mutant phenotypes), in animal experiments, and in human biomonitoring (particularly in relation to occupational exposure, and nutrition). Finally, DNA repair has been examined at the level of specific genome regions, using fluorescent *in situ* hybridisation with probes recognising different genes; it is clear that the rate of repair varies greatly between genes – as it does between people.

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