AbstractWe report measurements of the diffusion coefficient of β‐lactoglobulin A (βLG‐A) at pH = 5.60 and 4.58 in 0.10 ionic strength acetate buffer by the techniques of analog photocurrent signal correlation and digital single‐clipped photon correlation. At a concentration of 21 mg/ml and a pH of 4.58, the self‐association of β‐lactoglobulin can be represented by a simple dimer–octamer equilibrium model. We determined the translational diffusion coefficient of the dimer and that of the octamer using the scattering results of Kumosinski and Timasheff in a dimer–octamer mixture. Our analysis shows that the dimer βLG‐A does not change its size if the pH is varied from 5.60 to 4.58 and both species remain constant in size for temperature changes from 3.5° to 25°C Hydrodynamically, the octamers behave like closed‐packed spheres with an effective radius of about 45 Å according to the