Sixty-four patients took part in a cohort study measuring the efficacy of daily hormonal therapy in diminishing intestinal bleeding from small bowel angiodysplasia. Thirty patients received 5-10 mg norethynodrel either with mestranol, 0.075-0.15 mg (24 patients) or with conjugated estrogens, 0.625 mg (six patients). The cohort group consisted of 34 patients who either refused hormonal therapy (six patients) or were diagnosed early in our experience, before the resurgence of hormonal therapy (28 patients). Mean follow-up was 15.6 months (range 2-31 months) for the treated group and 13.4 months (range 1-23 months) for the untreated group. In addition, the change in monthly transfusion requirement with therapy was analyzed ("within group" analysis). Fifty percent (15 of 30) of the treated group required no further transfusion during therapy, while 44% (15 of 34) of the untreated group required no further therapy (not significant). During therapy, the mean monthly transfusion requirement of packed red blood cells in the treated group was not significantly different from that found before therapy (1.5 vs. 2.2 units, NS) or from that of the control group (1.5 vs. 1.6 units, NS). The findings do not support the use of hormonal therapy for bleeding from small intestinal angiodysplasia.