Abstract
Type-specific antibodies often do not appear in the blood serum of patients ill with pneumococcal pneumonia and treated with sulfapyridine until several days after the temp. has fallen to normal. Evidence is presented that type-specific antibodies play an important role in the process of recovery from pneumococcal pneumonia following treatment with sulfapyridine. The lateness of the appearance of circulating antibodies is offered as a possible explanation for the relapses which frequently occur when sulfapyridine therapy is discontinued too soon.