This multicentre, double-blind, placebo controlled, between-patient study in general practice in the United Kingdom examined the effect of oral N-acetylcysteine (Fabrol) on the symptomatology of patients with chronic bronchitis over a 3-month period. Although improvement in subjective symptoms (sputum viscosity and character, difficulty in expectoration and cough severity) occurred in both treatment groups over the trial period, improvements in difficulty in expectoration and cough severity were greater in patients receiving N-acetylcysteine compared to matching placebo. Trial medication was well tolerated, with a greater number of side-effects attributed to therapy occurring in patients receiving placebo.