The behavior of droplet swarms in liquid-liquid dispersions, especially found in extraction columns, are analyzed by a new fluorescence measurement technique which represents an extension to the capillary suction method. The measuring principle developed benefits from detectable-emission light intensity of a fluorescent dye even in a trace concentration. The addition of this nontransferring dye to the dispersed phase enables in situ determination of bivariate drop-size/drop-concentration distributions, which provides important information on droplet history for the evaluation of coalescence and breakup rates. Furthermore, the measuring method represents a new approach for the measurement of droplet-size-dependent residence times in extraction columns.