The clinical efficacy of LC9018, a biological response modifier prepared from heat-killed Lactobacillus casei YTT9018, used in combination with radiation was studied in a randomized controlled trial on 61 patients with carcinoma of the uterine cervix of Stage IIB or III. The combination therapy with LC9018 demonstrated a significant effect on tumor reduction, compared with radiation therapy alone, at the cumulative doses of 15-Gy and 30-Gy external irradiation (P less than 0.05). Histologic study confirmed that LC9018 also enhanced the therapeutic effect of the irradiation. Moreover, LC9018 seemed to be useful in protecting the patients from leukopenia during radiotherapy. This study suggests that LC9018, when used in combination with radiotherapy, will be an effective adjuvant immunotherapeutic agent. More studies in a large series of patients will, however, be needed to establish its long-term efficacy, safety, and effects on both prognosis and enhancing radiotherapy.