The Black Women's Health Study (BWHS), the largest follow-up study for cancer in African American (AA) women, began in 1995 when 59,000 women (median age, 38) from across the U.S. enrolled. The BWHS has successfully followed participants with biennial questionnaires for data on incident disease and medical, reproductive, behavioral, psychosocial, and socioeconomic factors, linked addresses to U.S. census data, and are currently linking to air pollution data. Cancer diagnoses are validated by pathology data from hospitals and cancer registries. A DNA bio repository was established through collection of cheek cell samples from 26,800 participants. Despite initial slow accrual of cancers due to the young age of participants at entry, the BWHS has published extensively on risk factors for breast cancer; sufficient cases of lung cancer, colorectal cancer, and colon adenomas are now available. We propose to (1) continue follow-up/data collection; (2) establish a repository of 17,800 blood samples; (3) share data/samples in consortia projects. Continuation of the BWHS is highly desirable: 90% of participants are still cancer-free; follow-up has been successful and unbiased; the cohort has reached ages at which cancer incidence increases markedly; effects of exposures (e.g., severe obesity, racism) that are less common in other populations can be studied; the DNA has made valuable contributions to genetic cancer studies and is a major replication source for studies of breast cancer and related phenotypes in AA and other groups; the BWHS is a key contributor to consortia projects of rarer cancers in /As; and the BWHS has been highly productive. Because levels of many blood markers are unfavorable among AAs and few studies of blood biomarkers in relation to cancer incidence have been carried out specifically in /As, we propose to establish a repository of blood samples in the BWHS. A successful pilot study demonstrated the feasibility of our methods and participation was unbiased and similar to that in other large follow-up studies. The repository will increase by 60% the limited number of AA women with available blood samples being followed in U.S. cancer cohort studies. AA women continue to be disproportionately affected by many cancers. Continuation of the BWHS will permit continuation of its valuable contributions to understanding cancer etiology in this understudied group. A blood repository will greatly increase the value of the BWHS resource by permitting studies that help to fill the knowledge gap about the relation of biomarkers to cancer incidence and survival in AAs. The assessment of serious nonmalignant illnesses in the BWHS enhances the value of this resource at no cost to the study of cancer.