In an attempt to confirm three reports suggesting a causal link between rauwolfia antihypertensive drugs and female breast carcinoma, all cases of such cancer appearing among the residents of an affluent retirement community were compared with controls chosen from a roster of all women in the same community. Most residents use a single care facility, and patterns of hypertension diagnosis, rauwolfia and other drug use, and medical-care-system patronage were abstracted from medical records. The prevalence of recorded rauwolfia use among the controls were 20 per cent, and that of other drug use was correspondingly high. The risk ratio for rauwolfia use was estimated to be 1.2 (95 per cent confidence interval, 0.7 to 2.2). Risk ratios between 1.0 and 2.0 were also found for other drug use and for measures of care-system patronage. These results do not support the hypothesis that reserpine causes breast cancer.