The fluorescence quenching of the 1-methylpyrene-N,N-dimethylaniline exciplex by quaternary ammonium salts is used to probe the formation of reversed micelles in BHDC-benzene-water solutions. The fluorescence of the exciplex is dependent on the BHDC concentration and the water content. A Stern-Volmer plot shows the existence of three regions for the fluorescence quenching. They are associated with the presence of BHDC ion pairs at very low concentrations, truly reversed micelles at concentrations higher than 0.02 M, and a transition region at intermediate concentrations.