We investigated the effect of adenosine 5¢-triphosphate (ATP), a-tocopherol and H 2 0 2 on the micropropagation of cucumber (Cucumis sativus L.) from nodal explants. The effect of the size of the liquid culture vessel (250-ml flask vs. 2.5-l airlift bioreactor) was also evaluated. The addition of ATP alone caused a significant increase in the number of branches (internodes) and in internodal length, but also a reduction of leaf number, compared to control cultures. It also increased significantly the accumulation of NO 3 À and K + . The application of ATP + a-tocopherol was associated with a significant increase in bud, internodal, leaf and petiole number, internodal, petiole and root length, as well as plant fresh weight, but reduced PO 4 3À and Ca 2+ accumulation. The combined application of ATP + a-tocopherol + H 2 O 2 was associated with maximum petiole length and increased plant fresh weight but reduced Ca 2+ accumulation. Compared to all other treatments, application of ATP + a-tocopherol in bioreactor-incubated cultures produced significantly larger plants, with an increased bud number, internode lenght and soluble carbohydrate concentration, but also with a reduced fresh weight, root length and reduced NO 3 À and PO 4 3À and Ca 2+ concentrations. These effects were associated with changes in the redox status of the regenerants, as well as dehydrogenase and peroxidase activities. The perspective for an application of ATP and antioxidants as novel, cost-efficient growth regulators in the micropropagation of this commercially important vegetable species is discussed.Abbreviations: Asc -ascorbate; ATP -adenosine 5¢-triphosphate; H 2 DCF-DA -2¢, 7¢-dichlorofluorescein diacetate; HPLC -high pressure liquid chromatography; MS -Murashige and Skoog basal medium (1962); PPFD -photosynthetic photon flux density; TTC -triphenyl-tetrazolium chloride