Abstract:The distribution of 6-methoxy-2-benzoxazolinone (MBOA) which is induced by blue light stimulation in maize ( Zea mays L. ) coleoplile was investigated by HPLC analysis. The results showed that: 1. The MBOA content on the irradiated side of the coleoptile was 1.5 fold more than that on the shaded side. 2. There was little change of IAA on both sides of the coleoptile which was treated with phototropic stimulation. 3. The growing coleoptile bent towards the side which was treated with MBOA, 5,6-dimethoxy-2-benzoxazolinone (DMBOA) or 2-chloro-5,6-dimethoxy-2-benzoxazolinone ( C1-DMBOA). The above results indicated that the phototropic bending of the coleoptile was attributed to unequal distribution of MBOA.