The formation of complexes between trypsin (T) and soybean tripsin inhibitor (STI) was analyzed, using a two-channel IAsys+ optical biosensor. The temperature dependence of complex formation (with its major parameters--the association rate constants (k(on)), the dissociation rate constants (k(off)) and the equilibrium constants (Kp)) was determined. The equilibrium constants obtained well correlate with those obtained by other methods. The association rate constant for the binding of T/STI complex increased with temperature, while the dissociation rate constant practically remained unchanged. The association and dissociation rate constants activation parameters were calculated from their concentration dependence. Based on the temperature dependence the activation energy, enthalpy and entropy of complex formation were calculated. It was shown that the entropy component plays a key role in T/STI interaction.