Spontaneous bacterial peritonitis (SBP) is frequently associated with renal failure. This study assessed if systemic and hepatic hemodynamics are also affected by this condition. Standard laboratory tests, tumor necrosis factor alpha (TNF-alpha) in plasma and ascitic fluid, plasma renin activity (PRA) and norepinephrine (NE), and systemic and hepatic hemodynamics were determined in 23 patients with SBP at diagnosis and after resolution of infection. Eight patients developed renal failure during treatment. At diagnosis of infection, patients developing renal failure showed significantly higher values of TNF-alpha, blood urea nitrogen (BUN), PRA and NE, peripheral vascular resistance, and hepatic venous pressure gradient (HVPG) and lower cardiac output than patients not developing renal failure. During treatment, a significant reduction in cardiac output and arterial pressure and increase in PRA and NE, HVPG, and Child-Pugh score were observed in the first group but not in the second. Peripheral vascular resistance remained unmodified in both groups. Changes in PRA and NE correlated inversely with changes in arterial pressure and directly with changes in BUN, Child-Pugh score, and HVPG. Five patients in the renal failure group developed encephalopathy, and 6 died. In the group without renal failure, none of the patients developed encephalopathy or expired. In conclusion, patients with SBP frequently develop a rapidly progressive impairment in systemic hemodynamics, leading to severe renal and hepatic failure, aggravation of portal hypertension, encephalopathy, and death. This occurs despite rapid resolution of infection and is associated with an extremely poor prognosis.