The objectives of this research are to define the constant and variable region characteristics of human antibody to the capsular polysaccharide of Hemophilus influenzae type b. The immunoglobulin class, subclass, allotypes and light chain types of antibody will be studied. The variable region will be analyzed by isoelectric focusing, fine-specificity analysis, and reactivity to anti-idiotypes. Genetic markers will be correlated with these analyses to define genetic control. The results of this analysis may provide an understanding of infant unresponsiveness to this capsular polysaccharide and may dictate new approaches for circumvention of this problem.