Topically applied antifibrinolytic drugs may be of value in the control of bleeding in active ulcerative colitis. Any impairment of systemic fibrinolysis in this condition, however, is potentially harmful. Since pharmacokinetic data after the rectal administration of tranexamic acid are non-existent, plasma concentration and recovery in the urine were recorded after a single dose of 2 g tranexamic acid given rectally to five patients with ulcerative colitis and to five healthy volunteers. The median area under the curve was, for the volunteers, 7.64 mg/L x hr (range: 4.43-11.56) and, for the patients, 13.84 mg/L x hr (range: 9.32-50.22) (P less than .05). The median 24-hour recovery in the urine was 0.8% (0.3-1.1) and 2.7% (1.1-4.0), respectively (P less than .05). The median peak plasma concentration was, for the volunteers, 0.40 mg/L (range: 0.20-0.69) 6 hours after administration and, for the patients, 1.10 mg/L (range: 0.53-2.90) 5 hours after administration (P less than .05). The plasma concentrations and recovery in the urine that were observed in the patients and volunteers were low compared with those seen after oral intake of the same dose. The plasma concentrations did not reach levels that were considered liable to impair systemic fibrinolysis.