Plasma activity of myeloperoxidase (MPO), malondialdehyde (MDA) and 4-hydroxynonenal (HNE) was measured prior to any treatment in 50 consecutive stroke patients with acute cerebral ischaemia, as well as in 14 healthy control subjects. Mann-Whitney-Wilcoxon test for unpaired data showed greater values of MPO (p < 0.01), MDA (p < 0.01) and HNE (p < 0.05) in stroke patients compared with controls. Considering as covariates the level of consciousness (GCS < 9 vs > or = 9), possible sources of emboli (yes vs no), leukocyte count (< 10 x 10(9)/1 vs > or = 10 x 10(9)/1) and relevant comorbid diseases (yes vs no), exact multiple logistic regression analysis indicated that only the presence of possible cardiac sources of emboli was associated with changes in by-products of lipid peroxidation. If confirmed in a larger series of subjects, our results could have therapeutic implications, providing more support for the use of free radical scavengers in the acute care of stroke patients with a possible cardioembolic aetiology.