The pre-treatment labelling index (LI) was measured in 72 patients with carcinoma of the cervix. It was not correlated with patient age, stage of the disease or histological grade. 46 patients underwent hysterectomy after intracavitary irradiation with or without external radiotherapy. The mean LI in patients with tumour sterilization or microscopic residue was significantly higher than in patients with gross disease. These results suggest that tumours with low LI may be difficult to sterilize with conventional therapeutic measures, or that doomed cells may require several weeks to be eliminated in tumours with low LI.