The study has a case-control design. The Group Health Cooperative (GHC) computerized files will be used to identify postmenopausal women, aged 30 to 79 yrs, with incident myocardial infarction (MI) or stroke during 1/2000-12/2004. Population-based controls, sampled from the GHC enrollment files, will be frequency matched to cases by age, calendar year, and treated hypertension. Data collection will include medical-record review, telephone interview of consenting subjects, and venous-blood collection. Standard methods will be used to assay variant alleles. The GHC computerized pharmacy records will serve as the primary source of information about the use of HRT. Data analysis will involve restriction, stratification, and logistic regression. Case-control and case-only analyses are planned. There will be a total of 600 MI cases, 420 stroke cases and 1800 controls.