Abstract: Described is a method and reagent kit for the detection of an analyte in a sample liquid by agglutination, wherein the sample liquid is contacted with an agglutination reagent in a reaction vessel that contains an inert matrix to form a reaction mixture that is then subjected to centrifugation. The reaction between the analyte and the agglutination reagent is determined based upon the penetration of the agglutination reagent into the inert matrix. The agglutination reagent includes synthetic particles having an average diameter and specific density chosen such that the particles' sedimentation behavior towards the matrix is essentially the same as that of erythrocytes under the same centrifugal conditions. Preferably, the surfaces of the synthetic particles have ligand molecules immobilized thereon for binding to the analyte.