The fluorescence decay kinetics of excited probes confined with quenchers in micelles or other approximately monodisperse cells is considered under conditions when both probe and quencher may be exchanged during the lifetime of the excited probe. The exchange may occur either by migration or in processes where two cells make contact and exchange their contents. It is shown that the decay follows, as a good first approximation, an equation of the Infelta type (Infelta, P. P.; Grätzel, M.; Thomas, J. K. J. Phys. Chem. 1974, 78,190) but with a generalized interpretation of the parameters. From measurements of the fluorescence decay information on cell size, quenching rate in the cell, and rate of the exchange process may be obtained. The use of the method is illustrated by some results from measurements on the reversed micellar, or microemulsion, phase in the system Triton X-100-toluene-water.