Cell cycle and cell population characteristics, as obtained for head and neck cancers by flow-cytometry analysis of a single tumor sample, after in vivo bromodeoxyuridine (Burd) infusion, were proposed for their prognostic value and for their potentials for radiotherapy planning (conventional vs accelerated) and monitoring. DNA ploidy, the S phase fraction labeling index (LI), and duration (Ts) as well as cell population potential doubling time (Tpot) were measured in 42 head and neck squamous cell carcinoma patients and analyzed along with histopathological and clinical data. Twenty-seven patients received standard radiotherapy (70 Gy/35 fractions/7 weeks) whereas 15 patients were treated with the concomitant boost technique (75 Gy/40 fr/6 weeks). The univariate analysis of 31 patients, for whom all the cell kinetic parameters were available, indicated that local control probability was strongly affected by lymph node status (p = 0.05) and by potential doubling time (p = 0.04). Patients having tumor Tpot < 5 days had markedly lower two-year local control rate (13%) than patients with Tpot > 5 days (68%). Furthermore, tumors with Tpot < or = 5 days exhibited a trend toward better local control after concomitant boost regimen compared with the patients treated with standard regimen (p = 0.06). These preliminary results point out that Tpot could play a role as additional prognostic factor influencing disease outcome in head and neck carcinomas treated by radiotherapy. In patients with fast growth-rate tumors (Tpot < or = 5 days) a more aggressive radiotherapy combination or chemo-radiotherapy should be suggested.