['To determine the effects of Lactobacillus fermentum I5007 on the redox state of piglets oxidatively stressed with diquat.', 'Twenty-four, 28-day-old barrows were used in a 2\xa0×\xa02 factorial design experiment with the main effects being Lact.\xa0fermentum supplementation and diquat challenge. Half of the pigs (n\xa0=\xa012) were orally administered with 20\xa0ml of a solution containing 10(8\xa0) CFU\xa0ml(-1) of Lact.\xa0fermentum each morning of the 21-day trial, while the remainder received saline. On day 8, these two groups were further subdivided so that half of the pigs in each group (n\xa0=\xa06) were intraperitoneally injected with 10\xa0mg\xa0kg(-1) BW diquat, while the remainder received saline. The diquat-injected pigs had significantly poorer performance and increased levels of plasma cortisol, adrenaline, carbonyl and malondialdehyde. Lactobacillus fermentum supplementation significantly increased superoxide dismutase and glutathione and increased the ability to inhibit superoxide anion production in liver and muscle.'] Does dietary supplementation with Lactobacillus fermentum I5007 improve the anti-oxidative activity of weanling piglets challenged with diquat?