Experimental measurements of the solution-mediated transformation (SMT) of the metastable polymorph of DL-methionine (a-DL-met) into the stable polymorph (gamma-DL-met) in water were performed at 25 degrees C. These results were compared to models of the crystallization and the SMT of a-DL-met into gamma-DL-met that were developed using the concept of the population balance equation (PBE) applied to both of the polymorphs. The growth, dissolution, and nucleation kinetic expressions obtained in a previous work were used in the models. It was found that the PBE models did not satisfactorily describe the SMT process of DL-met when the measured crystallization and dissolution kinetics were used. There were large mismatches between the simulation and the experimental results. Modifying the model of the dissolution kinetics of alpha-DL-met enabled these mismatches to be lowered. The results showed that the SMT of DL-met is controlled by the rate of dissolution of alpha-DL-met.