The conventional method of ascitic fluid culture detects bacteria in only 42%-65% of patients who have neutrocytic ascites and suspected spontaneous bacterial peritonitis. In this study ascitic fluid was cultured by the conventional method as well as by a new method consisting of bedside inoculation of blood culture bottles with ascites. The conventional cultures grew bacteria in only 13 (43%) of 30 episodes of neutrocytic ascites, whereas the blood culture bottles grew bacteria in 28 (93%); this difference was significant (p less than 0.0001). The blood culture bottle method also resulted in more rapid detection of bacterial growth. The median concentration of bacteria in infected ascites was one organism per milliliter. Bedside inoculation of blood culture bottles with ascitic fluid is more sensitive than the conventional method in detecting bacterial peritonitis. The insensitivity of the conventional method is probably due to the low concentration of bacteria in infected ascites and the small volume of ascites cultured by this method.