The associations between habitual diet and a variety of markers of lipid peroxidation or oxidative stress in a group of 95 healthy comparatively young Finnish volunteers (24 male and 71 females) were investigated. The habitual diet of the subjects was evaluated with a 3-day food record. The following biochemical parameters related to lipid peroxidation or oxidative stress were measured: lagtime of Cu2+ induced LDL oxidation in vitro, lipid hydroperoxides and Schiff bases produced during the LDL oxidation test, malondialdehyde measured as thiobarbituric acid-reactive substances from native LDL and Cu2+ oxidized LDL, serum paraoxonase (PON) activity. Serum PON activity showed most constantly associations with habitual diet. PON activity correlated negatively (r=-0.31 to -0.37) with intake of vegetables, total and water-soluble fiber, as well as intake of beta-carotene. Highly significant difference (P=0.005) in PON activity between lowest (<135 g/day) and highest (>256 g/day) vegetable intake quartiles was found. Malondialdehyde levels showed conflicting associations with diet. The results suggest that the significantly lower PON activity associated with high vegetable intake needs to be studied further.