A method based on the aggregate to monomol emission ratio, I-aggr/I-monomol, was used to determine the minimal hydrotropic concentration (MHC) of aromatic hydrotropes. The main advantage of this method is that it does not require the use of probes or other additives, which might disrupt the aggregation process. Also, it relies on spectrophotometric measurements, which are more sensitive and less arduous than others, like conductivity, light scattering and surface tension. (C) 2007 Elsevier Inc. All rights reserved.