Levels of polyamines (agmatine, putrescine, and spermidine) in young developing seedlings of kaiware-daikon (Raphanus sativus L.) and the effects of polyamine biosynthesis inhibitors, namely difluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) were investigated.1. During seed-germination, a sharp rise and decline of agmatine and putrescine while an increase of spermidine were observed.2. Agmatine, putrescine, and spermidine contents in the seedlings and cotyledons gradually decreased throughout the growth period after germination.3. The putrescine level in the seedlings treated by DFMA as a specific inhibitor of argininedecarboxylase was reduced to 27% of the control. In contrast, DFMO as a specific inhibitor of ornithinedecarboxylase did not affect the putrescine level in the seedlings.These results suggest that the putrescine is mainly synthesized from arginine via agmatine in the seedlings.