The efficacy was studied of prophylactic antibiotics in preventing febrile morbidity in patients with carcinoma of the cervix undergoing intracavitary radium insertions. Of 93 consecutive patients who had completed external irradiation and two intracavitary radium insertions, 63 (67.74%) had fever over 37.5 degrees C and 19 (20.43%) had fever over 38 degrees C during radium insertion when prophylactic antibiotics were not given. When 3 gm cefoxitin was given over 24 hrs in divided doses as prophylaxis, 39 (41.93%) had fever over 37.5 degrees C and 8 (8.60%) had fever over 38 degrees C. The difference was found to be statistically significant for fever over 37.5 degrees C (p < 0.001) and fever over 38 degrees C (p < 0.05). There was no difference in the duration of fever in the two groups, but the use of antibiotic prophylaxis apparently decreased the need for subsequent therapeutic antibiotics from 13.98% to 4.30%. No difference in the febrile incidence was found when considering the size of the cervical tumour, the stage of the disease, or whether it was a first or second radium insertion, or whether the patient had her menopause already. Prophylactic antibiotics were also found to be more effective in preventing febrile morbidity over 37.5 degrees C in those receiving adjuvant chemotherapy as compared to the general study group (p < 0.025). We concluded that the use of prophylactic antibiotics has beneficial effect in decreasing febrile episodes during the period the radium was inserted, as well as in reducing subsequent need for therapeutic antibiotics, while its use in immunocompromised patients who are prone to sepsis may also be of advantage.