It has been suggested that conflicting findings regarding rauwolfia drugs as predisposing factors for breast cancer can be explained by the hypothesis that use for a long duration predisposes to breast cancer occurring after age 50. In a follow-up study of 2077 women who received prescriptions for rauwolfia drugs there was no excess risk for breast cancer diagnosed at age 50 or greater (morbidity ratio = 0.9 compared to 1.0 expected). In comparing 35 patients in this age group with 168 women who received rauwolfia but remained free of breast cancer, there was no excess risk for long (greater than or equal to 5 yr) duration of use (relative risk = 0.9). Thus, the hypothesis could not be confirmed in this study group. It is likely that the excess risk among long-duration rauwolfia users, if present at all, is less than 2-fold.