Rationale: Cough is the commonest complaint for which medical attention is sought and chronic cough can be both physically and mentally debilitating. There is currently no evidence supporting the use of anti-tussives in chronic treatment resistant cough. Objectives: We tested the hypothesis that morphine sulphate in the dose of 5 mg bd would bring about a reduction in cough frequency and severity in patients failing to respond to specific measures. Methods: Patients recruited from the Hull Cough Clinic were enrolled into a randomised double blind placebo controlled study using 4 weeks of slow release morphine sulphate and a corresponding period of matched placebo. An open labelled extension of the core study allowed dose escalation to 10 mg bd. Cough was assessed using the Leicester Cough Questionnaire, daily symptom diary and citric acid cough challenge. Results: 27 Patients completed the core study. A significant improvement of 3.2 points over baseline was noted on the Leicester Cough Questionnaire (p<0.01). A rapid and highly significant reduction by 40% in daily cough scores was noted among patients on MST (p<0.01). Objective testing of the cough reflex using citric acid cough challenge tests did not show any significant changes. 18 patients continued into the extension study. Two thirds of these patients opted to increase the morphine to 10mg bd. At the end of 3 months there was a similar improvement in cough between the 5 mg and 10 mg groups. Conclusion: Morphine sulphate is an effective anti-tussive in intractable chronic cough at the doses of 5-10 mg bd.