Bleomycin, a natural antibiotic toxic to dividing cells, has been successfully used in combinations for treatment of recurrent head and neck cancer. In this study, we investigated five recently established head and neck squamous cell cancer lines (UT-SCC-2, UT-SCC-8, UT-SCC-9, UT-SCC-12A, UT-SCC-19A) in terms of response to bleomycin and radiation treatment. Experiments were carried out using the 96-well plate clonogenic assay for concentration determinations causing 20% (IC20), 50% (IC50), and 90% (IC90) inhibition of clonogenic survival and dose-response calculations for bleomycin. Survival fraction after a radiation dose of 2 Gy (SF2) was used as a measure for radiation sensitivity. The sensitivity for bleomycin was in good accordance with radiation sensitivity except for cell line UT-SCC-9. This was the cell line most sensitive to radiation (SF2 = 0.25 +/- 0.03) but was fairly resistant to chemotherapy (IC50 = 11.5M). Sensitivity patterns may suggest partly different mechanisms of action.