Using hysterectomy specimens obtained 1 month after Cf-252 neutron brachytherapy plus fractionated radiotherapy, we determined the fraction of positive and negative specimens with neutron dose for bulky Stage IB cervical cancers. The specimens obtained and studied after an initial Cf-252 insertion when the sources were newer and less decayed were more frequently negative for histological evidence of cancer than after the sources had decayed and 2 insertions were needed. After two insertions to deliver a therapeutic dose preoperatively the specimens were more frequently positive. When a larger initial dose was delivered to the tumor a larger proportion of negative specimens was noted. The size of neutron dose fraction was important to local tumor clearance and to rendering the specimens negative as well as schedule in use.