The comet assay is one of the most widely used methods to evaluate DNA damage and repair in eukaryotic cells. The comets can be measured by software, in a semi-automatic or automatic process. In this paper, we apply the CellProfiler open-source software for automatic analysis of comets from digitized images, reporting the percentage of tail DNA. A side-by-side comparison of CellProfiler with CASP software demonstrated good agreement between the two packages. Our work demonstrates that automatic measurement of silver-stained comets with open-source software is possible, providing significant time savings. © 2012 Elsevier B.V.