The authors present the interest of electrosyneresis for diagnosis of purulent meningitis. Test material is a study about 120 cerebrospinal fluids. Electrosyneresis sometimes permits to identify the germ when microscopic examination and culture are negative or when microscopy is positive and the culture negative. Application of electrosyneresis is still limited in France by the small immunogenicity of the specific polysaccharide of Neisseria meningitidis serotype B. principal etiologic agent of purulent meningitis, that do not allow, at present, to obtain suitable serums.