In cirrhotic patients with gastrointestinal hemorrhage, bacterial infections are frequent and play a significant role in mortality. We have previously found that patients with a Child-Pugh's class C or a rebleeding are a subgroup of cirrhotic patients with a high risk of infection. The aims of the study were (1) to validate these indicators and (2) to assess the effectiveness of a systemic antibiotic treatment in preventing bacterial infections in bleeding cirrhotics with a high risk of infection. One hundred and nineteen bleeding cirrhotic patients were divided into 3 groups. Patients with a Child-Pugh's class A-B and no rebleeding (i.e., with a low risk of infection) constituted group 1 (n = 55). Patients with a high risk of infection were randomly allocated to serve as controls (group 2, n = 34) or to receive the ciprofloxacin and a combination of amoxicillin and clavulanic acid for 3 days after hemorrhage (group 3, n = 30). This antibiotic prophylaxis was administered first intravenously and then orally when the bleeding was controlled. The study period was defined as 10 days after hemorrhage. Incidence of bacterial infections was significantly higher in patients from group 2 than in patients from group 1 (52.9% vs. 18.2%; P < .001). Moreover, infections were more severe in group 2: a sepsis syndrome or a septic shock developed in 66.7% of infected patients from this group, but in only 20% of infected patients from group 1. Incidence of bacterial infections was much lower in patients from group 3 than in those from group 2 (13.3% vs. 52.9%; P < .001). Eight patients from group 2 (23.5%) and 4 patients from group 3 (13.3%) died during the first four weeks (P-not significant). Septic shock was the cause of death in 3 patients from group 2 and in only 1 patient from group 3. The cost of antibiotic therapy, including antibiotic prophylaxis in group 3, was $208 +/- $63 per patient in group 2 and $167 +/- $42 per patient in group 3 (P < .05). We conclude that (1) patients with a Child-Pugh's class C and/or a rebleeding are a subgroup of cirrhotic patients with a high risk of infection after gastrointestinal hemorrhage and that (2) in these patients, a prophylactic treatment with systemic antibiotics is very effective in preventing bacterial infections.