The combination therapy of immunoglobulin preparations and antibiotics was carried out against the severe infections post neurosurgical operation to compare the difference of clinical efficacy between the two dosage schedules: the simultaneous combination therapy (Group A) and the non-simultaneous combination therapy (Group B). The common parameters for infections, body temperature, CRP and WBC monitored for their decrease rates over time course. As a result, significantly (p < 0.05) more rapid decreases of the body temperature, CRP and WBC were noted in Group A compared to Group B. Furthermore, the duration of treatment for Group A was shorter than that for Group B. Based on the result, it is suggested that the immunoglobulin preparations, simultaneously combined with the antibiotics, exert far more potent efficacy against the severe infections and shorten the treatment period, which may lead to reduction of medical costs as well as improvement of prognosis and QOL (quality of life) of the patients.