Steady-state fluorescence and time-resolved fluorescence have been used to study sodium deoxycholate aggregates at basic pH. Pyrene was used as a probe, and dimethylaniline, as a quencher. It is concluded that dynamic quenching with partially micellized quenchers and not static quenching with the quencher totally micellized, as has been often quoted in the literature, must be considered to interpret the experimental results. Fluorescence lifetimes for pyrene in the absence of quencher and the kinetic constants involved in quenching by dimethylaniline are given and compared to those for similar systems. The derived aggregation number, equal to 8 +/- 2, is close to the ones determined by other authors from freezing point depression and static light scattering. The possible distortion of these small aggregates by probes is also discussed.