A surface plasmon resonance (SPR) biosensor technology has recently been applied biochemically and clinically to the study of immunologic recognition and the evaluation of binding parameters for various interactions between antibodies (Abs) and antigens (Ags) at liquid-solid interface. The simple interaction between hapten and Ab fragment, e.g., variable single-chain fragment and antigenbinding fragment, can be described sufficiently by a 1:1 stoichiometry in SPR. However, the determination of the binding constant of an anti-protein Ab is usually complicated by the multivalence of the protein Ag. The SPR-based method enables direct determination of binding constants for a variety of specific Ab-Ag interactions in real-time. It also allows estimation of the binding stoichiometry and binding ratio for low-, intermediate-, and high-affinity Ab-Ag interaction systems. The present review is designed to indicate the theoretical background of SPR-based biosensor technology as well as to present the great variety of measurement modes of interaction kinetics that can be performed with these techniques. Quantitative aspects of the Ab-Ag interaction kinetics are reviewed, focusing especially on mono- and multi-valent Ab-Ag interaction modes using a SPR biosensor. Four model binding systems developed recently for use with SPR biosenser are described with principles and examples: (i) one to one interaction mode, (ii) nonequivalent two-site interaction mode, (iii) multiple equivalent-site interaction mode and (iv) multisite interaction mode. This article closes with two descriptions of the determinations of the binding stoichiometry and maximum binding ratio of Ab-Ag interactions.