Spontaneous bacterial peritonitis in cirrhosis is a serious complication that demands urgent attention. We report here a prospective study of the treatment of 27 episodes of spontaneous bacterial peritonitis in 22 cirrhotic patients with amoxicillin and clavulanic acid. The infection of ascitic fluid was diagnosed by a positive culture plus an ascitic neutrophil count exceeding 75/microliters, or by an ascitic neutrophil count exceeding 500/microliters. The infection was treated with 1 gm amoxicillin and 0.2 gm clavulanic acid every 6 hr for 14 days. In 17 cases (63%), bacteria were isolated from the ascitic fluid. All the bacteria isolated were sensitive to amoxicillin and clavulanic acid, whereas in five cases they were resistant to amoxicillin alone (Escherichia coli in two cases, Klebsiella pneumoniae in two cases and Bacteroides fragilis in one case). Cure of the infection was achieved in 23 episodes (85%) after 14 days' treatment; 17 patients (63%) were able to leave the hospital. Fourteen of 20 patients (70%) treated for the first episode of infection died within 1 yr: eight from infection, two from gastrointestinal hemorrhage, one from infection and hemorrhage and three from tumors. One patient who had repeated infections underwent liver transplantation and has not had any infectious complications 1.5 yr after surgery. Amoxicillin and clavulanic acid may be an effective first-line therapy for ascitic fluid infection in cirrhosis. Nevertheless, the 1-yr prognosis continues to be grave and the severity of the underlying liver disease remains the most important determinant for survival.