The aim of this work was to discover to what extent cigarette smoking and oral contraceptives, either separately or in association, are responsible for platelet adhesiveness changes in humans. Platelet adhesiveness has been measured in 77 subjects, smokers and nonsmokers. 47 of these subjects were women both using and not using oral contraceptives. Cigarette smoking significantly increases platelet adhesiveness both in men and women. On the contrary, if no distinction is made in the smoking habits of female volunteers and they are only divided into two groups according to the use or nonuse of oral contraceptives, no significant change in platelet adhesiveness occurs following intake of oral contraceptives.