Cinobufagin is a cardiotonic steroid that has been found in the skin of toads of genus Bufo and has diverse biological activities.^1,2,3,4 It inhibits Na+/K+-ATPase activity in guinea pig heart ventricular muscle homogenates by 45% when used at a concentration of 0.3 μM.¹ Cinobufagin is cytotoxic to HCT116 colorectal cancer cells in vitro with IC50 values of less than 50 ng/ml at 48- and 72-hour time points and induces apoptosis in a concentration-dependent manner.² In vivo, cinobufagin (10 mg/kg) reduces tumor growth in an HCT116 mouse xenograft model. Cinobufagin (1 μg/ml) inhibits LPS-induced expression of MHC class II, CD80, and CD86 and release of IL-6, IL-8, TNF-α, and IL-10 in human monocyte-derived dendritic cells.³ It also increases expression of the antimicrobial peptides hBD2 and hBD3 in dendritic cells. Cinobufagin exhibits dose-dependent antinociceptive effects in the hot-plate, acetic acid writhing, and formalin tests in mice.⁴