Critical concentrations, aggregation numbers, and effective micellar charges of the amphiphilic drug propranolol hydrochloride have been determined from static light scattering measurements at 25 degrees C in the presence of added electrolyte (0.0-0.5 mol kg(-1) NaCl). Photon correlation spectroscopy (dynamic light scattering) has shown an increase in micellar size with an increase of added electrolyte concentration. To quantify the interaction between aggregates, the correlation data have been interpreted by the DLVO theory. Micellar properties have been determined by the application of mass action theory to the concentration dependence of H-1 NMR chemical shifts confirming the results obtained by light scattering.