Effect of evening primrose oil (EPO) was assessed on coagulation parameters following 30 and 60 days administration of 90, 180 and 360 microl/kg oil to healthy rabbits of either sex. There was significant increase in all assays except Fibrinogen time. These effects might be due to inactivation or inhibition of factors affecting coagulation. The intake of evening primrose oil also significantly decreased platelet count. Results of this study suggest that evening primrose oil shows considerable anti-anticoagulant and anti-platelet activity in animals and has potential to reduce cardiovascular morbidity and mortality.