Tiotropium bromide is a new long-lasting anticholinergic drug which, like ipratropium bromide, is a quaternary ammonium derivative. It binds with high affinity to muscarinic receptors but dissociates very slowly from M(1)- and M(3)-muscarinic receptors. Pharmacology studies have demonstrated a prolonged protective effect against cholinergic agonists and cholinergic nerve stimulation in animal and human airways. In Phase II studies single inhaled doses of tiotropium bromide have a bronchodilator and bronchoprotective effect in asthmatic and chronic obstructive pulmonary disease (COPD) patients of over 24 h. In Phase III studies, once daily inhaled tiotropium is an effective bronchodilator in COPD patients, giving great improvement in lung function and reduction in symptoms than ipratropium bromide given four times daily. The drug is well-tolerated and the only side effect of note is dryness of the mouth which occurs in approximately 10% of patients. Since, anticholinergics are the bronchodilators of choice in COPD it is likely that tiotropium bromide will become the most widely used bronchodilator for COPD patients in the future.