An increased generation of reactive oxygen species occurs during exercise. We investigated whether changes in plasma antioxidants and lipid oxidation products after submaximal resistance exercise are detectable, and whether training status has any effect on changes. Seven resistance trained (RT, 31.3 +/- 10.2 yrs) and ten non-resistance trained male subjects (NRT, 28.2 +/- 3.9 yrs) performed a submaximal resistance exercise circuit (10 different exercises, 75% of 1-repetition maximum, 18.6 +/- 1.1 minutes). Blood samples were taken before and immediately after exercise. Plasma antioxidants (AO), lipid oxidation products malondialdehyde (MDA) and conjugated dienes (CD) were measured using HPLC and/or photometric detection. Groups were compared using the Mann-Whitney U test, the exercise effect was tested using the Wilcoxon signed ranks test. P < 0.05 was regarded as significant. alpha-Tocopherol, gamma-tocopherol, beta-carotene, lycopene, ascorbic acid,MDA and CD concentrations did not differ between groups at rest. There was a similar increase of fat soluble plasma AO in both groups after exercise, but not ascorbic acid. MDA increased also in both groups after exercise, but CD increased only in NRT. There is no difference in plasma AO and lipid oxidation products in RT and NRT at rest. After short time resistance exercise there is a mobilization of fat soluble AO. Despite mobilization of AO, oxidative stress occurs during submaximal resistance exercise, which is indicated by increased MDA and CD concentrations. As exercise induced an increase of CD only in NRT, it seems that regular resistance training partly prevents lipid peroxidation during exercise.