Time-resolved and steady-state fluorescence have been employed to study the fluorescence quenching of pyrene, solubilized in novel micelles of the zwitterionic surfactant, N-(3-dodecyloxy-2-hydroxy propyl)-N,N-dimethylglycine (DHDG), by iodide ions in aqueous solution. The fluorescence quenching rate constants (k(q)), micellar exit rate constants (k(-)), and micellar aggregation numbers (N) have been determined in each case. Generally the fluorescence quenching rates in micellar solutions with pH values above the isoelectric point (pH 5.1) (zwitterionic) of DHDG are lower than when pH is below 5.1 (cationic). Addition of NaCl results in a moderate variation of the micellar aggregation numbers and a subsequent change in k(q). When cationic and zwitterionic DHDG micelles have the same micelle aggregation number, k(q) in the cationic DHDG micelles is higher, suggesting that both the aggregation number and. the micellar surface potential related to the charge of head groups influence k(q). The dynamics of iodide ion exit from DHDG micelles has also been studied. The exit rate constants of iodide ion from micelles, k(-), is independent of micelle concentration (in the range studied), but is dependent on micellar aggregation number and is related to micellar interfacial potential. The steady-state and time-resolved fluorescence measurements agree very well, suggesting the importance of dynamic fluorescence quenching processes.