Abstract: A method for the flow cytometric assay of an analyte using monodisperse particles carrying a specific binding partner, the analyte and binding partner being selected from the group consisting of (a) antigen and specific antibody, (b) hormone and hormone receptor, (c) hapten and antihapten, (d) polynucleotide and polynucleotide binding protein, (e) biotin and avidin or streptavidin, (f) enzyme and enzyme cofactor and (g) lectin and specific carbohydrate, and the method comprising the steps of adding to the aqueous sample a predetermined amount of particles and a predeterminded amount of a labelled ligand having affinity for the analyte or the binding partner and detecting and quantifying the resulting labelled ligand-carrying particles by a flow cytometer, the method using a pair of different particle types which are distinguishable from each other by the flow cytometer and which respectively carry binding partners having the same specificity but different binding affinity for the analyte and independently but

Abstract: Device for liquid flow cytophotometer including a device for hydrodynamic focussing (4,6) of a cell- or particle-suspension towards a measuring area, and an optical excitation-and detection-system (9), preferentially based on oil immersion optics, characterized by the focussing device being formed at or in relation to the system's optical axis-rotating nozzle assembly (1) directed towards a surface (7) which is open in relation to the surrounding atmosphere and situated on the optics (9), forming the optics' measuring area, thus supplying a laminar liquid flow of the above-mentioned suspension.