While varying levels of expression were observed, all markers were relatively sensitive requiring as little as 1ng of RNA input into the reverse transcription (RT) reaction. In singleplex reactions, seven of the eight analyzed blood markers (all except AQP9) demonstrated a high degree of specificity for blood. In multiplex reactions, non-reproducible cross-reactivity was observed for several of the mRNA markers, which was reduced and, in most cases, eliminated when less input total RNA was used. Additionally, some cross-reactivity was observed with tissue and animal samples. Despite differences in the observed sensitivity and specificity of the blood markers examined in this study, a number of the candidates appear to be suitable for inclusion in appropriately validated multiplex mRNA-based body fluid identification systems. (Published Abstract)