In theory, the best possible detection limit of a FISH analysis is restricted through the amount of sample which is applied on the slide or analysed in a flow cytometer. FISH performed on glass slides usually allows for an application volume of about 10–30 μl of sample. Assuming the spotting of 10 μl of (untreated or concentrated and pretreated) sample per slide as an example, this would set the theoretical detection limit at roughly 100 cells/ml. This optimistic estimation requires the highly efficient fixation, permeabilization and hybridization as well as the complete assessment of the entire slide.