1. Oxitropium bromide (Oxivent), an anticholinergic bronchodilator, inhibits coughing induced by hypotonic aerosols in both asthmatic and non-asthmatic individuals. We have now extended this work to investigate whether this antitussive activity is reproducible in cough associated with viral infection. 2. The effect of oxitropium bromide (200 micrograms three times daily) on cough and pulmonary function has been studied in 56 non-asthmatic volunteers with upper respiratory tract infections (URTI) in a double-blind, randomised, parallel group, placebo controlled study over 10 days. 3. Lung function, symptom questionnaire and cough response to ultrasonically nebulised distilled water (UNDW) inhalation were initially recorded within 72 h of development of cough and again after the 10 day treatment period. By use of a diary card at home, frequency and severity of cough, nocturnal symptoms and general malaise were assessed daily throughout the treatment period using 5 cm visual analogue scales (VAS). Peak expiratory flow rate (PEFR) was recorded thrice daily before treatment over this 10 day period. 4. VAS scores of symptoms and UNDW-induced cough frequency all decreased over the 10 days of observation whether oxitropium bromide or placebo was administered. The mean PEFR showed a statistically significant fall in morning values during the early stages of infection which lessened with recovery but no effect of treatment with oxitropium bromide was observed (P > 0.05). 5. Oxitropium bromide, which inhibits the cough response to UNDW, does not offer an effective therapy for cough associated with an upper respiratory tract viral infection.