Addition of an electrolyte such as NaCl to ionic micelles such as sodium dodecyl Sulfate (SDS) alters the ionic atmosphere of the bulk solvent, thereby changing both the micellar properties and the interaction pattern of micelles with a molecule in the solvent. In this study, we show how added NaCl in the presence of SDS micelles modulates the surface charge of the micelles, which in turn fine-tunes the switchover equilibrium between anionic and global neutral forms of piroxicam. The presence of salt alters the CMC and aggregation number of SDS micelles. The binding of the global neutral form of piroxicam with SDS is found to be strongly modulated by the presence of counterion in the bulk solvent. (c) 2005 Elsevier Inc. All rights reserved.