Counterimmunoelectrophoresis (CIE) is described as a rapid and specific method for early detection of bacterial antigens. This simple and reliable technique was applied to samples of serum and cerebrospinal fluid (CSF) from 67 patients in whom neonatal septicemia or bacterial meningitis was initially suspected. Seven out of 11 patients with culture-proven bacterial infections had positive CIE determinations before results of routine microbiological cultures were available. CIE was especially helpful in children treated with antibodies prior to admission. All negative CIE results in proven bacterial infections were due to non-available antisera for the specific antigens detected by routine blood or CSF cultures. Shortcomings of the method and a future CIE diagnostic program are discussed.