PIP: In view of the controversy stemming from reports indicating young women who take combined types of oral contraceptives are at greater risk of venous thrombosis and cerebral or coronary thrombosis, a clinical investigation of blood coagulation changes among 41 oral contraceptive users and 25 controls was undertaken at the K.E.M. Hospital in Bombay, India. The 25 controls (Group A) were women who planned to begin using oral contraceptives but had not yet begun use. 16 of the 41 oral contraceptive users had been taking combined pills for 1 l/2 - 5 years (Group B) and the other 35 for more than 5 years (Group C). Coagulation parameters investigated were 1) prothrombin time; 2) partial thromboplastin time; 3) serum fibrinogen; 4) euglobulin clot lysis time; 5) platelet count; 6) platelet adhesiveness; and 7) platelet aggregation. Significant changes occurred in partial thromboplastin time, platelet count, platlet aggregation, and prothrombin time. Group B had a higher rise in prothrombin time than Group A and a rise in platelet aggregation and in partial thromboplastin time compared to Group A. Platelet counts were higher for both groups of oral contraceptive users than for the controls.