Flow cytometry analyses of tumors from 12 patients with cervical squamous cell carcinoma under radiotherapy were performed in this preliminary study. Six patients with a high (> 10%) G2/M fraction before treatment showed greater than 50% tumor reduction after initial 2000 cGy radiotherapy. Only two out of six patients with a low (< 10%) G2/M fraction before treatment responded favorably and three of them already had recurrence during the follow-up period of 33-40 months. Hyperploidy (DNA index > 1.1) was observed in 5 patients; all of them responded well to radiotherapy in contrast to three out of seven diploid tumors.