The effective charge of bovine serum albumin in aqueous solution is determined by dynamic NMR as a function of pH. The effective charge results from the degree of dissociation varying with pH and the local counterion condensation. While the hydrodynamic friction is determined from the diffusion coefficient measured by pulsed-field gradient NMR, the electrophoretic mobility is determined by electrophoresis NMR. The effective charge per molecule is calculated from the force balance between hydrodynamic friction and force in the electric field acting on the charges. Since it is influenced by counterion condensation it is smaller than the net charge from titration. (c) 2006 Elsevier B.V. All rights reserved.