The free polyamine content of flag leaves, peduncles, rachis, glumes, and grains of wheat (Triticum aestivum L., cv. Castell) plants, ripening under field conditions, has been investigated during three consecutive growing seasons. Putrescine was quantitatively the most important of all polyamines detected in these organs. Concentrations were highest in the grains, glumes and flag leaves. No correlation was found between polyamine content and the onset of senescence of flag leaves and other organs. Excised primary leaves, however, showed a decrease in polyamine content in the dark and also in light/dark cycles, but in the latter case only after an initial increase. Sink removal of otherwise intact wheat plants caused an accumulation of putrescine in flag leaves at the later stages of senescence, whereas removal of all other leaves was without any significant effect. Putrescine was also recovered in phloem-exudate samples collected throughout the period of grain development. In both grains and glumes, peak concentrations of polyamines were found early during seed development.