Cigarette-smoking is a well-established aetiological factor in squamous cell carcinoma of the larynx. In Great Britain the majority of patients with laryngeal cancer are treated by radiotherapy with salvage surgery if necessary. A troublesome side effect of radiotherapy is mucositis which may exacerbate hoarseness, dysphagia, airway obstruction or pain. Although it is a common belief that continued smoking and alcohol consumption during radiotherapy may increase the frequency and severity of these side effects this has not been demonstrated objectively. This study confirms and illustrates the relationship between such radiotherapy reactions to continued smoke exposure by using an objective biochemical marker of smoking status.