The unusual polyamines, sym-homospermidine (homoSPD) and canavalmine (CAN), were found in the seed of Canavalia species such as C. gladiata, C. ensiformis, and C. brasilensis, but not in those of other leguminous crops. To examine the distribution and metabolism of homoSPD and CAN in sword bean, C. gladiata cv Shironata, polyamine analysis was carried out throughout the life cycle of this plant. During seed germination, putrescine (PUT), spermidine (SPD), and spermine (SPM) were accumulated in the radicle and hypocotyl. HomoSPD and CAN were, however, maintained at very low levels over a 6-day period of germination. In nodulated sword bean plants, a large quantity of homoSPD was found in the root nodule. CAN was detected exclusively in the senescent nodule at very low concentrations. These polyamines were not detected in any other organs including root, stem, leaf, vine, flower, and pod, while PUT, SPD, and SPM were always found in those organs. As plants reached the reproductive stage, homoSPD and CAN appeared in the immature seed and their concentrations increased as seed formation progressed. By contrast, the level of SPM continuously decreased during seed development. In developing seeds, considerable accumulation of canavanine, an analog of arginine, which is a precursor in polyamine biosynthesis, was also observed.