ABSTRACT The kinetics of ninhydrin--amino acid (alanine, phenylalanine, and valine) reaction have been studies in the absence and in presence of a common hydrotrope, sodiumbezoate. A strong enhancement in the rate of reaction has been observed in the presence of the hydrotrope above its minimal hydrotrope concentration (MHC). The order of reaction in ninhydrin was always found to be unity while that in amino acid decreases from unity to zero at higher Aminoacid]. A mechanism consistent with kinetic data and involving the formation of a mixed aggregation assemblies between amino acid and hydrtotrope has been proposed.