In addition to their beneficial effects in reducing platelet responsiveness, it has been a matter of controversy whether polyunsaturated fatty acids impair the fibrinolytic system or not. In a double-blind, parallel clinical trial, 40 subjects were randomized to treatment with 6 g/day of corn oil, or to 6 g/day of a fish oil preparation, enriched with omega-3-polyunsaturated fatty acids (2.0 g/day of omega-3-PUFA). Clinical and fibrinolytic variables were measured before and after 5 months of treatment. In the corn oil group, plasminogen activator inhibitor (PAI-1) decreased significantly but in the cod liver oil group, PAI-1 remained unchanged. Activities and mass concentrations of tissue plasminogen activator (t-PA) were unchanged in both groups. It is concluded that, in the doses given here, both these preparations have small or no effects on the fibrinolytic system.