The seaweed concentrate (SWC) Kelpak ® is made from Ecklonia maxima (Osbeck) Papenfuss and is used as a biostimulant in agriculture. Cytokinins and auxins have been identified in Kelpak ® and are partly responsible for the growth-promoting effects observed. Other biologically active compounds such as polyamines (PAs) might also be present in the SWC. A study was carried out to investigate the PA levels in E. maxima and Kelpak ® . The stipes, fronds, and SWC prepared from E. maxima were collected monthly over a 2-year period. Extracts were benzoylated, and endogenous PAs were quantified using high-performance liquid chromatography. Putrescine concentrations ranged from 6.10 to 40.40 μg g -1 dry weight (dw), from 15.98 to 54.46 μg g -1 dw, and from 0.98 to 5.51 μg ml -1 in the stipe, fronds, and SWC, respectively. Spermine concentrations ranged from 1.02 to 35.44 μg g -1 dw, from 1.05 to 27.35 μg g -1 dw, and from 1.27 to 4.95 μg ml -1 in the stipe, fronds, and SWC, respectively. Spermidine concentrations fell below the detection threshold. This is the first report of PAs being detected in a SWC. The seasonal pattern established for the stipe, frond, and SWC followed the same trend over a biennial cycle, with PAs accumulating in the seaweed tissue during periods of active growth and during periods of rough wave action (stress response).