Abstract In previous reports (1, 2) a technic was outlined by which certain neurotropic viruses (St. Louis Encephalitis and murine-adapted strain of Lansing Poliomyelitis) may be adsorbed to the surface of heat-killed bacterial cells (Serratia marcescens) and subsequently agglutinated by specific hyperimmune serum and by the convalescent serum of patients infected with the homologous virus. The test was designated as the Bacterial Agglutination (B.A.) Method for the detection of virus-related specific humoral factors. The validity of this reaction has been confirmed with experimental poliomyelitis (SK strain) in the monkey in which the initial appearance of this agglutinating factor in the blood stream was observed as early as the second day after inoculation (3). Weil (4) has confirmed the observation that viruses may be adsorbed by heat-killed bacterial cells and such cells specifically agglutinated by an antiserum homologous to the adsorbed virus.