Steady-state and time-resolved fluorescence have been used to study the gelation of sodium deoxycholate at pH values close to neutrality. Pyrene was used as a probe. The results suggest the formation of pyrene excimer as a result of the aggregation process : when two clusters carrying probes form a larger one, pyrene molecules can interact in both the ground and excited states. Fluorescence lifetimes for monomer and excimer pyrene are given and favorably compared to similar systems. A structure for the aggregates is also suggested.