The Virotag® DY reagents stain viral genomes and viral envelope proteins with a combination of two fluorogenic dyes. When fluorescent emission is simultaneously observed in both channels of the Virus Counter system, this ‘simultaneous event’ is counted as one intact particle. Due to its universal mechanism, the Virotag® DY ENV dye is compatible with all enveloped viruses. The reagent is ready-to-use in a simple, no-wash labeling protocol for virus samples. After 30 min incubation, the stained samples can be quantified on the Virus Counter® platformReagent kits contain all staining reagents and solutions needed to measure the indicated number of samples.