Carboxylated poly(styrene/acrylamide) [P(St/AAm)-H] latex particles with relatively high hydrophilicity and colloidal stability were prepared by emulsifier-free emulsion polymerization. Various amounts of antibodies against hen egg-white lysozyme (HEL), bakers yeast invertase, ovalbumin and bovine serum albumin (BSA) were covalently immobilized onto the latex particles by the carbodiimide method. The initial rates of the immunological agglutination of these antibody-immobilized latex particles by the addition of antigens were quantified by the absorbance changes at a wavelength of 680 nm. The immunological agglutination rates showed a similar tendency irrespective of the antigen-antibody system. That is, the initial agglutination rate (i) increased with at. increasing amount of immobilized antibody, (ii) was largest at an ionic strength of approximately 0.1 at pH 7.0, and (iii) decreased with increasing pH. These tendencies were similar to those in the immunological agglutination of antigen-immobilized latex particles by the addition of antibodies. Based on these results, the main factors which control immunological agglutination rates are discussed.