A recently-identified secreted form of luciferase also serves as a useful reporter for HTS assays. Luciferase from the marine copepod, Metridia longa, has unique secretary features that make it suitable for extracellular reporter assays. Markova et al. reported the substrate specificity of Metridia luciferase (MetLuc) and demonstrated its suitability for use as a reporter for monitoring gene expression [16] . In common with SEAP, secreted MetLuc is well suited to monitoring gene expression in time-course reporter assays. Both SEAP and MetLuc are currently available in a commercial dual reporter system that has been successfully applied in drug screening research [17] [18] [19] [20] .