[en] Platelet factor 4 (PF4) monomers (7,800 daltons) form dimers and tetramers in varying molar ratios under certain solution conditions. The presence of a simplified aromatic region (one Try and two His) and resolved monomer, dimer, and tetramer Y60 3,5 ring proton resonances makes study of PF4 aggregate association/dissociation thermodynamics and kinetics possible. PF4 protein subunit association/dissociation equilibrium thermodynamic parameters have been derived by ¹H NMR (500 MHz) resonance line-fitting analysis of steady-state Y60 3,5 ring proton resonance monomer-dimer-tetramer populations as a function of temperature from 10 to 40 C. The thermodynamic parameters are consistent with low dielectric medium electrostatic/hydrophobic interactions governing dimer formation and hydrogen bonding governing tetramer formation. Association/dissociation kinetic parameters, i.e., steady-state jump rates, have been derived form exchange-induced linme-width increases and from ¹H NMR (500 MHz) saturation-transfer and spin-lattice (T₁) relaxation experiments. From dissociation jump rates and equilibrium constants, association rate constants were estimated. Kinetically, tetramers are preferred over dimers due primarily to a slower dissociation rate, and thermo-dynamically, tetramer formation is enthalpy-driven, while dimerization is entropy-driven