Our patient presented with severe respiratory distress and marked pleocytosis. She was mechanically ventilated and received gamma globulin with high titers of anti-pertussis toxin and anti-filamentous hemagglutinin. Her clinical signs improved and a notable decrease in white blood cell count was observed. Ten months after treatment, the patient showed normal physical and mental development and anti-pertussis toxin and anti-filamentous hemagglutinin titers were significantly increased. Recently, the effectiveness of gamma globulin therapy has been emphasized again. Our experience supports the use of iv gamma globulin infusion. Also, gamma globulin did not influence the patient's own immunologic response to pertussis. Gamma globulin therapy with high anti-pertussis toxin titers could be considered for treatment of severe pertussis.