We present the application of hydration forces to obtain high sensitivity IgG±latex immunosystems. To compare these with another standard system, a study is presented of IgG± and F(ab') 2 ± latex conjugates in terms of colloidal stability and immunoreactivity. The stability domains have been examined using a low-angle light scattering technique (nephelometer). The protein-coated particles present an anomalous stability at high ionic strength when the classical theory predicts aggregation, and this stabilization is attributed to hydration forces. Different electrolyte concentrations and counterion valences have been tested to determine the most in¯uential factors on this stabilization mechanism. Long-term aggregation of the conjugates has also been studied by measuring the aggregate size by photon correlation spectroscopy. To quantify the immunoresponse of the agglutination tests, aggregation in the presence of antigen is followed as a function of time with the nephelometer. The considerable increase in immunoresponse, together with the decrease in possible perturbing side-reactions enhances the technical interest of this method of stabilizing immunolatexes.