A case of spontaneous bacterial peritonitis (SBP) developed in an old man whose ascitic fluid was related neither to portal hypertension nor nephrotic syndrome, but with severe hypoalbuminemia emerged after a massive bleeding from a gastric ulcer in a malnutrition state. Ascitic fluid, increasing day by day, yielded Enterobacter cloacae and Bacteroides fragilis. Though autopsy was not carried out because of refusal of his family, neither liver necropsy, nor abdominal CT scan nor repeated abdominal ultrasonography showed findings suggesting existence of liver cirrhosis. In the presence of his ascites, the extent of a chemiluminescence (CL) response of polymorphonuclear cells from volunteers was significantly lower than that of his serum. This report shows that SBP can develop in a patient with ascites unrelated to portal hypertension when ascitic fluid induces little CL response.