A process for the quantitative optical analysis of fluorescently labeled biological cells involves contacting a cell layer on a transparent support at the bottom of a reaction vessel with a solution containing the fluorescent dye. This process can also be used for improving the sensitivity in the quantitative optical analysis of a luminescent biological cell layer. Analogously, these process principles can also be used in receptor studies for the masking of the interfering background radiation in the quantitative optical analysis of fluorescently or luminescently labelled reaction components. In this case, a receptor layer at the bottom of a reaction vessel is in contact with a solution in which a fluorescent or luminescent ligand is dissolved.