Rationale: Soluble guanylyl cyclase (sGC), a cyclic guanosine 5 ́-monophosphate (cGMP) generating enzyme, regulates smooth muscle tone and exerts anti-inflammatory effects in animal models of asthma and acute lung injury. In Chronic Obstructive Pulmonary Disease (COPD), primarily caused by cigarette smoke (CS), lung inflammation persists and smooth muscle tone remains elevated, despite ample amounts of nitric oxide (NO) that could activate sGC. Objective: To determine the expression and function of sGC in patients with COPD and in a murine model of COPD. Methods: Expression of sGCα1, α2 and β1 subunits was examined in lungs of never smokers, smokers without airflow limitation and patients with COPD; and in C57BL/6 mice after 3 days, 4 and 24 weeks of CS exposure. The functional role of sGC was investigated in vivo by measuring bronchial responsiveness to serotonin (5- HT) in mice using genetic and pharmacological approaches. Measurements and Main Results: Pulmonary expression of sGC, both at mRNA and protein level, was decreased in smokers without airflow limitation and in patients with COPD, and correlated with disease severity (FEV1%). In mice, exposure to CS reduced sGC, cGMP levels and protein kinase G activity. sGCα1-/- mice exposed to CS exhibited bronchial hyperresponsiveness (BHR) to serotonin. Activation of sGC by BAY 58-2667 restored the sGC signaling and attenuated BHR in CS-exposed mice. Conclusions: Downregulation of soluble guanylyl cyclase due to cigarette smoke exposure might contribute to airflow limitation in COPD.