Genipin, the aglycone of geniposide, is metabolically produced from the geniposide in body tissues. The purpose of this study is to clarify some pharmacological actions of genipin. Genipin showed concentration-dependent inhibition on lipid peroxidation induced by Fe++/ascorbate in rat brain homogenate. Genipin exhibited significant topical antiinflammatory effect shown as an inhibition of croton oil-induced ear edema in mice. Nitric oxide (NO) synthesis by inducible nitric oxide synthase (iNOS) is increased in inflammatory diseases and leads to cellular injury. Genipin concentration-dependently (50-300 microM) inhibited NO production and iNOS expression upon stimulation by lipopolysaccharide/interferon-gamma (IFN-gamma) in RAW 264.7, a murine macrophage cell line. Genipin markedly blocked lipopolysaccharide-evoked degradation of inhibitor-kappaB-beta (IkappaB-beta), indicating that it exhibits inhibitory effect on NO production through the inhibition of nuclear factor-kappaB (NF-kappaB) activation. It was also shown to contain potent antiangiogenic activity in a dose-dependent manner, which was detected by chick embryo chorioallantoic membrane assay. In summary, we demonstrate that genipin possesses antiinflammatory and is a specific hydroxyl radical scavenger. Its antiangiogenic and NO production-inhibitory properties are also presented.