An unusual chlorinated 1,4-benzoxazin-3-one derivative has been isolated from young corn roots. Its structure was established by spectroscopic techniques (lH-, 13C-NMR, EI and CI-MS, UV and IR) and by correlation with known benzoxazinone derivatives. The assignments of all protons could be made by 1 H shift-correlated 2-D NMR techniques. The chlorinated benzoxazine derivative has been confirmed to be naturally occurring in a second carefully planned growth-chamber experiment.