Our general objective is to determine, by means of an epidemiologic case-control study if exposure of hair dyes or menopausal estrogens significantly increases a woman's risk of developing breast cancer. Special emphasis will be placed on evaluating dose-rfesponse and latency. The hypothesis that benign breast disease and exposure to hair dyes or menopausal estrogens combine to significantly increase a woman's risk of developing breast cancer will be refined and assessed. This study has also been designed to examine the epidemiologic characteristics of women with estrogen positive and negative breast cancers. Approximately 2000 female patients with primary carcinoma of the breast will be available for study. This sample size will provide an adequate test of the overall hypothesis including a detailed analysis of dose-response and latency. The sample size will also allow separate analyses of the major histologic subtypes and analysis of potential interactions between hair dyes, menopausal estrogens and benign breast disease. Demographic, pathologic and clincal data will be collected from the hospital records of each patient, utilizing a standardized abstract form. Epidemiologic data will be collected through telephone interviews with each patient and control. Key data obtained from the interviews will be validated through comparison with hospital and physician records.