Systemic infections caused by certain encapsulated bacteria are accompanied by release of capsular polysaccharide. Immunologic detection of such antigens in body fluids is a potentially valuable tool for rapid diagnosis. We propose to develop this approach for use in the diagnosis of childhood meningitis, an infection generally caused by H. influenzae, N. meningitidis, or D. pneumoniae, all of which have well- described capsular antigens. The methods to be evaluated for assay of CSF and serum are countercurrent immunoelectrophoresis (CIE) and latex agglutination (LA). Both systems have the speed, simplicity and reproducibility necessary for an acceptable diagnostic test. In the present state of development, CIE is not sufficiently sensitive to detect all culture-positive cases. LA, though amply sensitive, is hampered by non-specific positive reactions and by the instability of antibody-sensitized test particles. We intend to study the system variables that are likely determinants for these shortcomings. Thus for CIE, antiserum potency, pH and ionic strength of buffer, type and concentration of gel matrix, and voltage will be evaluated. For LA, the problematic factors are the purity of antibody used to sensitize the latex particles, as reflected in the ratio of immunoglobulin to other serum proteins and the ratio of specific to non-specific immunoglobulin; the buffer system as it affects the sensitization process and the test procedure; the identity of non- specific agglutinating factors in specimen fluids and means for selective elimination of such factors. Cross reactions among bacterial polysaccharides are germane to either methodology. The relevant cross reactions will be identified and absorption procedures to circumvent them will be elaborated. After optimal test conditions and reagents are devised with the use of purified antigens, the methodology will be evaluated by retrospective testing of a bank of clinical specimens.