YC-1 is an NO-independent activator of soluble guanylyl cyclase. It inhibits collagen (10 µg/ml) and thrombin (0.1 U/ml) induced platelet aggregation with IC50 values of 11.7-14.6 and 57.3-59.3 µM, respectively. In the absence of NO or CO, 200 µM YC-1 increases the activity of purified soluble guanylyl cyclase 12-fold, with an ED50 value of 20 µM. At a concentration of 200 µM, YC-1 potentiates the maximal activity of soluble guanylyl cyclase in the presence of NO or CO by 40% and >3,000%, respectively.