Platelet hyperactivity, resulting in platelet adhesion to the vessel wall, is one of the most important factors responsible for thrombosis and the incidence of cardiovascular diseases. In this study we were aimed to investigate and compare the inhibitory effects of the methanol extracts of three herb species on adhesion of the activated platelet to laminin-coated plates, aggregation and protein secretion. Artemisia dracunculus (tarragon), Satureja hortensis (summer savory) and Origanum majorana (marjoram) are used as blood anti-coagulator in Iranian folk medicine. Human platelets were prepared and incubated with different concentrations of the test samples (equivalent to 50-200 microg of each of the plant leaves powder/mL) for 60 min. The treated and untreated platelets were then activated with thrombin (0.25 U/mL) and their adhesion to laminin-coated plates was investigated. Based on our observations, the methanol extract of A. dracunculus, S. hortensis and O. majorana, at a concentration of 200 microg/mL, inhibited platelet adhesion to laminin-coated wells by 51%, 48% and 40%, respectively. In addition to alternation of cell adhesive properties, self aggregation and protein secretion of the treated platelets were also affected upon treatment with the crude methanol extracts. These observations provide the basis for the traditional use of these herbs in treatments of cardiovascular diseases and thrombosis.