Experiments were carried out to make clear relationship between the flower bud formation and the endogenous auxin-like substance levels in the Japanese radish, Raphanus sativus L. cultivars 'Wase-shijunichi' and 'Hayabutori-tokinashi.' Vernalization was performed for 20 days at 5℃ before sowing. Those seedlings precedingly vernalized and non-vernalized were grown at the same time in the continuous artificial illumination room at 25℃. Auxin-like substances in acidic fraction were extracted from leaves and stems at various growth stages of both vernalized and non-vernalized plants and activities were bioassayed by the Avena coleoptile straight growth test. Preceding flower bud formation, the activities of auxin-like substance exhibited at the lowest levels in chilling treated plants on the both cultivars of 'Wase-shijunichi' and 'Hayabutori-tokinashi.' The auxin-like substance levels of the former cultivar falled down immediately, whereas that of the latter 10 days after sowing time. It is very important and interesting phenomenon that the activities of endogenous auxin-like substance decline before flower bud formation in each cultivar.