Abstract Genotyping error, often associated with low-quantity/quality DNA samples, is an important issue when using genetic tags to estimate abundance using capture-mark-recapture (CMR). dropout, an MS-Windows program, identifies both loci and samples that likely contain errors affecting CMR estimates. dropout uses a ‘bimodal test’, that enumerates the number of loci different between each pair of samples, and a ‘difference in capture history test’ (DCH) to determine those loci producing the most errors. Importantly, the DCH test allows one to determine that a data set is error-free. dropout has been evaluated in McKelvey & Schwartz (2004) and is now available online.