A study in humans demonstrated that the expression profiles of piwi-interacting RNA (piRNA) provide valuable information for discriminating forensically relevant biological fluids [Wang et al. DOI:10.1016/j.fsigen.2019.07.015]. A study in humans using massively parallel sequencing identified the piR-hsa-28033 as an absolute specific marker for semen, demonstrating high specificity in all five pairwise comparisons and high expression levels [Liu et al. DOI:10.3390/genes13091530].