The use of the SNAP-ChIP panels also allows to determine the optimal antibody concentration. Although often ignored, optimization of the antibody concentration can be crucial for highly specific ChIP and ChIP-seq results. Even with a very specific antibody, using a suboptimal concentration could be detrimental for the results. Using too much antibody may result in an increase of the background and thus a decrease in specificity, whereas insufficient antibody might result in a decrease of the recovery and possibly the loss of less enriched regions. It is therefore very important to determine the best compromise between recovery and specificity. To establish this, titration of our antibodies in ChIP is a standard procedure in our antibody validation pipeline. Until recently, the optimal antibody concentration was determined based on the +/- control ratios and the amount of IP’d DNA, sometimes supplemented with bioinformatic analysis of the ChIP-seq results. This method, however, mainly allows to estimate general background and not actual cross reaction. Using the SNAP-ChIP panel, we can now determine the actual effect of antibody concentration on cross reaction with other modifications (Fig. 1).