To define the anti-allergic components in Saiboku-To, a herbal medicine for bronchial asthma, we examined the effects of 11 compounds found in post-administrative urine of Saiboku-To on concanavalin A-induced human lymphocyte blastogenesis in vitro and picryl chloride (PC)-induced mouse ear swelling in vivo. The urinary products of Saiboku-To were flavonoids and lignans derived from the constitutional herbs and their hydrogenated metabolites. Medicarpin derived from Glycyrrhiza glabra, magnolol and 8,9-dihydroxydihydromagnolol from Magnolia officinalis, baicalein, wogonin and oroxylin A from Suctellaria baicalensis inhibited lymphocyte blastogenesis in dose-dependent fashion with IC50 values ranging from 3.0 to 7.7 micrograms/mL, which corresponded to 20-100 times that of prednisolone IC50 (0.08 microgram/mL). Davidigenin, dihydrowogonin and dihydrooroxylin A, which are hydrogenated metabolites of liquiritigenin, wogonin and oroxylin A, respectively, had no or little effects on lymphocyte blastogenesis. Oral administration of Saiboku-To, medicarpin, baicalein, magnolol and baicalin (100 mg/kg), inhibited PC-induced ear swelling significantly by 23.5, 40.1, 30.5, 23.6 and 20.9%, respectively, though the effects were weaker than that of 5 mg/kg of prednisolone (52.9%). The results suggested that flavonoids and lignans tested in the present study were implicated in anti-asthmatic effect of Saiboku-To through suppression of type IV allergic reaction.