Dynamic light scattering (DLS) theory for particle sizing relies on the infinite dilution assumption, which assumes that the scattering behavior of particles can be attributed to their independent, translational Brownian motion, not to attractive or repulsive intermolecular interference. This assumption is especially relevant for ELPs in general, and KI8 in particular, due to the tendency of ELPs to self-associate and the tendency of similarly-charged proteins to experience repulsion. To determine the validity of the infinite dilution assumption for the system under study, we measured the concentration-dependence of the hydrodynamic diameter (DH) and translational diffusion coefficient (DT) of KI8. We performed DLS on serial dilutions of KI8 under four conditions of varying pH and salt (NaCl) concentration (Figure ). We found DH ≈ 15-26 nm in 10 mM HEPES pH 7.4, 15 mM or 150 mM NaCl, with no clear trend as a function of concentration. This size measurement likely corresponds to dynamic, soluble monomers of KI8, as it falls between the predicted size of a 39 kDa folded globular protein (~2 nm) and the size of a fully extended beta strand conformation of 460 amino acids (161 nm). We also found that in 10 mM CAPS pH 11.2, 15 mM or 150 mM NaCl, the predominant species detected were greater than 100 nm, indicating the greater tendency of these samples to assemble. We hypothesize that this tendency to assemble persists even at lower concentrations because these samples were prepared by dilution of a stock initially dissolved at a concentration of 2 mg/mL, promoting self-assembly through concentration effects. Samples initially dissolved in these same conditions at 0.4 mg/mL were later seen to have nanometer-scale DH values. We interpret the possible outliers at 0.25 mg/mL as potentially resulting from nearing the lower limit of the concentration range for accurate measurements.