We previously reported that Sairei-to concentration-dependently modified lipopolysaccharide (LPS)-stimulated prostaglandin E(2) (PGE(2)) production in mouse macrophage-like RAW264.7 cells. Among twelve major ingredients of Sairei-to, Scutellariae radix inhibited the LPS-stimulated PGE(2) production to the greatest extent, followed by Zingiberis rhizoma, Glycyrrhizae radix, Atractylodis lanceae rhizoma and Pinelliae tuber. Scutellariae radix contained several major flavonoids such as baicalin, baicalein and wogonin. We investigated the effect of these flavonoids on PGE(2) production and COX-2 expression by LPS-activated RAW264.7 cells. Wogonin inhibited PGE(2) production most efficiently, followed by baicalein and then baicalin, in the same order as their membrane permeability. It was unexpected that wogonin and all other compounds would fail to inhibit the expression of COX-2 at both protein and mRNA levels, suggesting the importance of re-evaluating the point of action of wogonin.