Taking into account the energy vs. distance functions of the aspecific (macroscopic) repulsion that usually prevails between antigen (Ag) and antibody (Ab) molecules in polar media, as well as the specific (microscopic) attraction between epitope and paratope of Ag and Ab, it proved possible to determine the kinetic constants (von Smoluchowski, 1917;Hammes, 1978) of Ag-Ab interactions, from the surface properties of Ag, Ab and the aqueous medium. The kinetic constants thus found correlate well with experimentally determined kinetic constants in comparable systems, and confirm the importance of the influence of the concentration of one of the reagents (e.g. the Ab) on the kinetic association constant (Van Regenmortel et al., 1994), which is largely due to steric hindrance. Applying the same energy vs. distance approach to the influence of temperature (T) on Ag-Ab reactions, it ensues that the familiar occurrence of an apparent 'enthalpy-entropy compensation' in aqueous media is in fact the relatively gratuitous outcome of a complex set of effects caused by an increase in T, on the total free energy, the hydration energy and, as a result, on the inter-epitope-paratope distance. A close correlation exists between the outcome of these surface-thermodynamic analyses and experimental results.