['To elucidate the anti-allergic and anti-inflammatory effects of Petasites genus, we studied the effects of several compounds isolated from Petasites japonicas leaves.', 'Bakkenolide B was isolated from Petasites japonicus leaves. Antigen-induced degranulation was measured in RBL-2H3 mast cells by measuring β-hexosamidase activity. Induction of inducible nitric oxide synthase and cyclooxygenase 2 was measured by Western blotting in peritoneal macrophages. Ovalbumin-induced asthma model was used for in vivo efficacy test of bakkanolide B.', 'We found that bakkenolide B, a major component of the leaves, concentration-dependently inhibited RBL-2H3 mast cell degranulation. Bakkenolide B also inhibited the gene inductions of inducible nitric oxide synthase and cyclooxygenase 2 in mouse peritoneal macrophages. Furthermore, in an ovalbumin-induced asthma model, bakkenolide B strongly inhibited the accumulation of eosinophils, macrophages, and lymphocytes to bronchoalveolar lavage fluid.'] Does anti-allergic and anti-inflammatory effects of bakkenolide B isolated from Petasites japonicus leave?