4-Methylthio-3-butenyl isothiocyanate as the direct precursor of raphanusanins has been isolated from the commercially available radish (Raphanus sativus L.), and some chemical studies on 4-methylthio-3-butenyl isothiocyanate (MTB-ITC) have been carried out, where it has been spontaneously converted into raphanusanins, phototropism-regulating substances of radish hypocotyls, in MeOH-H₂O as well as in H₂O solution.