A homogeneous fluorescent binding assay method comprising the steps of: • providing carrier particles in solution with at least one binding site on each of said carrier particles; • providing at least first and second components; with the first being a substance to be tested, the second being tagged with a fluorescent substance; • exposing said carrier particles to the first and second components, to cause a reaction between said first and/or second components and said at least one binding site on said particles; whereby the number of fluorescently tagged components to said carrier particles changes and wherein complexes between said fluorescently tagged components and said carrier particles are formed which are preferably diffusing within said solution; • illuminating the solution containing both the free and bound fluorescently tagged substances with optical radiation at a first wavelength to cause fluorescent output radiation at a second longer wavelength; • optically sensing output signals at said second wavelength resulting from said fluorescent output radiation by measuring in a repetitive mode a number of photon counts per time interval of defined length or by measuring in a repetitive mode a length of time intervals between preferably consecutive photon counts characterized in that said method further comprises the steps of • electronically processing the optically sensed signals to determine the amount of fluorescently tagged component which is free and/or that which is bound to the carrier particles without physically separating the free and bound fluorescent components, wherein said electronically processing the optically sensed output signals comprises the steps of determining a distribution function of the number of photon counts per said time interval and thereafter determining a distribution function of specific brightness of said carrier particles and/or said fluorescently tagged components on basis of said function of the number of photon counts; or determining a distribution function of the length of said time intervals and thereafter determining a distribution function of specific brightness of said carrier particles and/or said fluorescently tagged components on basis of said function of the length of time intervals. • providing carrier particles in solution with at least one binding site on each of said carrier particles; • providing at least first and second components; with the first being a substance to be tested, the second being tagged with a fluorescent substance; • exposing said carrier particles to the first and second components, to cause a reaction between said first and/or second components and said at least one binding site on said particles; whereby the number of fluorescently tagged components to said carrier particles changes and wherein complexes between said fluorescently tagged components and said carrier particles are formed which are preferably diffusing within said solution; • illuminating the solution containing both the free and bound fluorescently tagged substances with optical radiation at a first wavelength to cause fluorescent output radiation at a second longer wavelength; • optically sensing output signals at said second wavelength resulting from said fluorescent output radiation by measuring in a repetitive mode a number of photon counts per time interval of defined length or by measuring in a repetitive mode a length of time intervals between preferably consecutive photon counts characterized in that said method further comprises the steps of • electronically processing the optically sensed signals to determine the amount of fluorescently tagged component which is free and/or that which is bound to the carrier particles without physically separating the free and bound fluorescent components, wherein said electronically processing the optically sensed output signals comprises the steps of