Since oral contraceptives (OCs) were first marketed in the 1960's formulations have changed: overall, estrogen and progestogen doses have been decreased in hope of reducing the acute adverse effect of OC use on risk of cardiovascular disease. There are also new types of formulations (e.g., triphasics). Studies of formulations used in the 1970's indicated a 3-4 fold increase in the risk of myocardial infarction (MI) in current OC users relative to never users. There are no published data on OCs introduced since then. We are just completing data collection in a case-control study of MI in women under age 65. The primary aim was to assess whether long term OC use in the past increase the risk of MI. A projected, included in the study were 105 premenopausal cases (and 515 premenopausal controls) under age 45 (women aged 45 or more now rarely use OCs): for current OC users relative to never users, the estimated relative risk of MI, controlling age and smoking, was 1.7(95% confidence interval, 0.5-5.8). This result is compatible with no adverse effect of the newer OCs or a smaller effect than that of older formulations; but it is also compatible with an effect as large. We propose to continue to study women under age 45 using the network of 60 hospitals in Massachusetts and Rhode Island set up at great cost for our study of past OC use. We will add 35 hospitals in Pennsylvania, a network used successfully in our previous study of MI and current OC use conducted in 1976-1979. In the proposed study, an additional 225 cases and 1125 controls will be interviewed; these, combined with the 105 cases and 515 controls on hand, will make a total of at least 330 premenopausal cases and 1650 premenopausal controls under age 45. This sample will permit definitive assessment of the effect on MI risk of current use of OCs presently in use: i.e., ruling out or establishing a 2-fold or more increased risk. It will also allow assessment of the effect of current OC use in smokers (who are already at increased risk of MI); data from earlier studies indicated that heavy smoking enhanced the adverse effect of OCs on MI risk. This information will be of value to women making choices about contraceptive practices, particularly since the IUD is no longer readily available and contraceptive alternatives are more limited than before.