PF-03635659 is a potent, very long dissociative half-life (slow off-rate, >1440 min) muscarinic M3 antagonist. Spirometry data from healthy volunteers in phase I clinical studies illustrate that PF-03635659 provides efficacious 24 h bronchodilation from a single inhaled dose, thus confirming the suitability of PF-03635659 as a novel once-daily inhaled muscarinic M3 receptor antagonist for the treatment of chronic obstructive pulmonary disease (COPD). Safety (tachycardia) and toleration (dry mouth) data from the multidose phase I studies indicate an adverse event profile that is at least noninferior to tiotropium bromide. PF-03635659 had been in phase II clinical trial for the treatment of chronic obstructive pulmonary disease.