Cough is a protective mechanism and an important symptom of many respiratory diseases. When coughing is only an annoying reflex and produces no mucus clearance, inducing fatigue or exhaustion for patients and worsening their pathological condition, antitussive drugs may be indicated.In this study we evaluated the efficacy and safety of moguisteine, a new antitussive drug with a peripheral mechanism of action, in a population of 124 adult patients with persistent cough associated with various respiratory disorders. Obstructive chronic bronchitis, reported in about 50% of the study population, was the most frequent underlying diagnosis. We conducted a randomised single-blind short term treatment trial in 7 centres, comparing moguisteine (3 doses of 200mg, over 2 days) to dextromethorphan (3 doses of 30mg, over 2 days). The primary efficacy variable was the percentage reduction in the audio tape-recorded number of coughs during a 6-hour period in the morning after the last dose of the study drug versus a 6-hour recording at baseline.Patients' subjectively assessed visual analogue scale (VAS) scores of cough frequency and cough troublesomeness at night and during the morning were considered as secondary efficacy variables.Safety was assessed by means of routine clinical laboratory tests and adverse event monitoring.The postdrug percentage reduction in the number of coughs approached 30% on either drug. VAS scores of cough frequency and cough troublesomeness showed remarkable reductions in both groups, without any noteworthy difference between treatments. Possible or probable drugrelated adverse events were reported in 3 of 61 patients on moguisteine (1 heartburn, 1 gastric pain, 1 diarrhoea) and in 4 of 63 patients on dextromethorphan (1 rhinitis and slight decrease of white blood cell count, 1 syncope, 1 gastric discomfort, 1 diarrhoea). Treatment discontinuation was necessary only for 1 patient, who had a syncope after the first dose of dextromethorphan.Our results indicate that treatment with moguisteine rapidly induces substantial cough relief and that it is well tolerated and as effective as dextromethorphan.