Selection of optimal biomarkers for the identification of different operational taxonomic units (OTUs) may be a hard and tedious task, especially when phylogenetic trees for multiple genes need to be compared. With TaxonGap we present a novel and easy-to-handle software tool that allows visual comparison of the discriminative power of multiple biomarkers for a set of OTUs. The compact graphical output allows for easy comparison and selection of individual biomarkers.