Complement 3 is an important component of ascitic fluid total protein, which offers local defence against infection of the ascitic fluid. Hepatic synthesis of complement 3 as well as other proteins and their concentrations in ascitic fluid is significantly reduced in patients with advanced cirrhosis. The level of protein in ascitic fluid in cirrhotic patients with spontaneous bacterial peritonitis was compared with that in patients without spontaneous bacterial peritonitis. Ascitic fluid protein level in spontaneous bacterial peritonitis (n=15) was 1.1 +/- 0.3 g/dL whereas it was 1.5 +/- 0.5 g/dL in patients without spontaneous bacterial peritonitis (n=15). In conclusion, this study suggests that, ascitic fluid protein level is significantly (p = 0.008) reduced in cirrhotic patients who develop spontaneous bacterial peritonitis.