['Leucoreduction of blood components, including platelet components, is strongly encouraged but not yet universal, especially outside high income countries. As both leucocytes and platelets secrete copious amounts of pro-inflammatory cytokines/chemokines under various conditions and during storage, we investigated the potential of the respective secretory programmes of these cells in order to evaluate their subsequent pathophysiological effects.', 'A total of 158 individual non-leucoreduced platelet components were obtained from Tunisian donors and tested for characteristic biological response modifiers (BRM) of leukocytes (IL-1β, IL-8), platelets (sCD62P, sCD40L) and both cell types (TNF-α, RANTES) in the presence or absence of thrombin stimulation and after different periods of storage (up to 5 days). BRM levels were determined using enzyme-linked immunosorbent assays and Luminex technology. Platelet-leucocyte aggregate formation during storage was analysed using flow cytometry.', 'Leucocyte- and platelet-associated BRM had clearly distinct profiles both at the onset (day 0) and termination (day 5) of the observation period but altered during the intermediate period so that their respective importance was inverted; in fact, the profiles were merged and indistinguishable on days 2-3. The leucocyte-derived BRM largely dominated over platelet-derived ones and further altered the BRM platelet secretion programme.'] Do leucocyte cytokines dominate platelet cytokines over time in non-leucoreduced platelet components?