Twenty-five patients with FIGO stage IIIB carcinoma of the cervix were entered into a prospective, double-blinded randomized study to evaluate the possible radiation potentiating properties (i.e., improved survival) of the S phase cell cycle specific inhibitor of DNA synthesis hydroxyurea (H). In contrast to our previous randomized trial of patients with FIGO stage IIIB carcinoma of the uterine cervix who were documented to be without paraaortic lymph node metastasis by pretherapy staging paraaortic lymphadenectomy [Piver et al.: J Surg Oncol 35: 129-134, 1987], these patients either refused surgical staging or, because of medical conditions, could not undergo pretherapy paraaortic lymphadenectomy. Patients were to receive 6,000 cGy/6 weeks to the pelvis by megavoltage radiation therapy followed by 2,500 cGy to point A by intracavitary and vaginal radium/cesium. The median pelvic cGy for the Hu patients was 5,967 cGy and for the placebo patients 6,013 cGy. Leukopenia (WBC less than 2,500/mm3) significantly increased in patients given hydroxyurea as compared with those given placebo (P less than 0.0001). There was no statistically significant difference relative to anemia, thrombocytopenia, radiation skin reactions, diarrhea, or radiation induced complications requiring surgical correction. The estimated 5 year disease-free interval was 54% for the hydroxyurea patients (median not reached) and 18% for the placebo patients with a median of 11 months. Because of these results, those of our previous reports, and those of the Gynecologic Oncology Group, we believe that hydroxyruea plus pelvic radiation should be the standard against which new potential radiation sensitizers are tested.