Forty-six tumors from patients with oropharyngeal carcinoma were analysed by flow cytometry after injection of bromodeoxyuridine (Budr) for the labelling index, the duration of S phase and the potential doubling time (Tpot). The results show large variations in Tpot (from 2.6 to 16.7 days) among these tumors from the same site and with the same histology. The variations in Tpot were not significantly related to TNM status and differentiation grade. However, aneuploid tumors had statistically significant shorter Tpot. The predictive value of Tpot regarding the response to radiotherapy is currently under investigation.