In this work the adherence of colloidal hematite to silver and mercury electrodes from 10(-2) M NaClO4 solutions was studied by direct counting on SEM micrographs and admittance measurements. A linear relationship was found between the particle coverage on the electrode and the difference of the electrode capacity in the colloidal suspension and that in the base electrolyte. A simple model which explains this relationship is proposed. The experimental results indicate the presence of specific interactions between hematite and the metallic surface.