The authors studied erythrocyte aggregation in 62 patients suffering from hemorrhoidal disease, distributed on the basis of proctoscopy findings between three groups (recent uncomplicated congestive attack, recent thrombosed hemorrhoid, stage IIb or III chronic prolapse). This hemorheological parameter is a sensitive marker of circulatory stasis. Values measured were compared with those obtained in 21 healthy subjects. Erythrocyte aggregation index was significantly higher in patients than in controls (31.6 +/- 6.8 versus 27.7 +/- 4.4) (p < 0.05). This difference was due essentially to increased values in patients with acute hemorrhoid problems. A parallel increase in blood fibrinogen was found in these same patients. Hemorheological changes could predispose to worsening of venous stasis in the hemorrhoidal circulation and participate in the onset or spread of thrombotic processes.