15520 Background: The optimum radiosensitizing dose and schedule of gemcitabine for squamous cell carcinoma of head and neck are not known. The objectives of this study were to evaluate the efficacy and toxicity of weekly gemcitabine as a radiosensitizer concurrent with radical radiotherapy in locally advanced head and neck cancer. Method: Thirty-nine patients with stage III or IV B inoperable carcinoma of head and neck were enrolled. Eligible patients had histopathologically confirmed squamous cell carcinoma with age between 18–70 years. Patients had a KPS >70 with an adequate marrow, hepatic and renal function. No prior chemotherapy or radiotherapy was allowed. Patients with nasopharyngeal, glottic or sub-glottic cancer were excluded. Gemcitabine 150 mg/m2 or a total dose not exceeding 200 mg was given on day 1,8,15,22,29, and 36 during radiation treatment. Gemcitabine was infused in 200 ml of normal saline in 2 hours and radiation was delivered two hours after the completion of gemcitabine infusion. Conventional fractionation was used to deliver a total dose of 66 Gy. CTC version 2.0 of NCI and RTOG/EORTC Late Radiation Morbidity Scoring Scheme were used for evaluation of toxicity and RECIST was used for response evaluation. Results: Only 35 patients were considered evaluable for response. Complete response was seen in 8 (22.9%) (95% CI; 10.4–40.1%), partial response in 25 (71.4%), with an overall response rate of 94.3% (95% CI; 80.8–99.3%). All the thirty-nine patients were evaluable for toxicity. Grade 3 and 4 mucositis was seen in 28 (71.8%) and 2 (5.1%) patients respectively. Grade 3 pharyngeal toxicity was seen in 6 (15.4%). One patient developed pharyngo-cutaneous fistula. Despite vigorous symptomatic and supportive care acute toxicities led to treatment interruption in 16 (41%) of patients. Conclusion: Weekly gemcitabine at a dose of 150mg/m2 concurrent with radiation therapy gives a high overall response rate and a high rate of acute toxicity. No significant financial relationships to disclose.