During the development of a therapeutic peptide or protein drug product one of the main aspects that the manufacturer has to evaluate is aggregation, especially when the protein is highly concentrated. Typically this assessment is focused on the evaluation of irreversible (i.e., covalent) aggregates. However, the characterization of reversible aggregates is also important since an increase of long lived reversible aggregates in IV formulations may lead to immugoenicity issues, affect PK/PD, and change bioactivity (due to change in secondary structure upon aggregation). The characterization of the aggregation behavior of a reversibly self-associating peptide is presented and the analytical challenges faced are discussed. The use of light scattering (dynamic/static), CD, native page, SEC (disruptive and nondisruptive conditions), and sedimentation velocity AUC were all used to ascertain the nature of the aggregates and the behavior of the peptide in solution at increasing concentrations.