Abstract: The present invention provides a FCCS method for determining the concentration and/or the diffusion coefficient of at least a first labeled species, a second labeled species and/or a complex between said first and second labeled species, in a system, wherein the method comprises the steps of determining a cross-talk parameter K, wherein K is the ratio between the brightness of the first labeled species and the second labeled species at the centre of each focus, as detected for both species in the channel for detecting the second labeled species; using the cross talk parameter K for determining a displacement parameter ro and using K, ro, or both K and ro for determining the concentration and/or the diffusion coefficient of said first and/or a second labeled species and/or a complex between said first and second labeled species.