Polyamines have been reported as efficient antioxidantcompounds in plants. Sunflower leaf discs, treatedwith 100 µM paraquat (PQ), a well known oxidativestress inducer, showed decreased levels of putrescine(Put), spermidine (Spd) and spermine (Spm) (between33% and 80% with respect to the controls). Argininedecarboxylase (ADC) and ornithine decarboxylase (ODC)activities decreased 42% and 33% respectively. Amongthe markers of oxidative stress measured after PQtreatment, chlorophyll and glutathione content werereduced (30% and 49% respectively) andthiobarbituric acid reactive substances (TBARS)content increased (60%). Superoxide dismutase (SOD)activity declined 60% with respect to the control andlipoxygenase (LOX) increased 25% when leaf-discs weretreated with the herbicide. Pretreatment withexogenous polyamines (1 mM) reversed paraquat toxicityto different degrees according to the polyamine and/orthe tested parameter. Spermidine was able to inhibitchlorophyll loss, while Spm reverted the effect of PQon the level of TBARS almost completely and alsorestored SOD activity close to control values.Putrescine was the least effective as an oxidantprotectant. These results provide support for theargument that polyamines are effective antioxidantsthrough their ability to act as radical scavengers.