Platelet aggregation induced by microbubbles (simulating microbubbles developing during deep sea diving or clinical situations such as extracorporeal circulation) in platelet rich plasma was measured in 11 male volunteers before and after intake of 15 ml seal oil(Pagophilus groenlandica)per day for 2 weeks. The relative content of arachidonic acid (AA) decreased in platelets from all individuals, whereas the content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) increased. Also in plasma, the relative content of EPA and DHA increased, while the change in AA content was small but variable. Generally, the platelet content of oleic acid increased while the linoleic acid decreased. Intake of seal oil decreased platelet aggregation induced by microbubbles. A significant correlation between aggregation in platelet-rich plasma (PRP) and the AA content in platelets was shown, while there was a significant negative correlation between oleic acid content and platelet aggregation. In whole blood, however, seal oil intake did not result in less platelet aggregation using ADP and U-46619 as agonists.