BACKGROUND: Spontaneous bacterial peritonitis(SBP) is an infection of ascitic fluid without any apparent intra-abdominal foci of sepsis. Although the definitive diagnosis of SBP requires a positive ascitic fluid culture, causative organisms are not isolated in up to 65% of patients with well defined SBP probably due to inadequate culture techniques. We compared two culture methods for ascites : conventional and blood culture method. METHODS: From June 1989 until December 1994, the blood culture method of ascitic fluid culture was performed(Group A). Ascitic fluid was inoculated at the bedside directly into one aerobic and one anaerobic BACTEC blood culture bottles. During the period from January to December 1995, ascitic fluid was processed by the conventional culture method of inoculating a sample of ascitic fluid on sheep blood agar, MacConKey agar, brucella agar and into thioglycolate broth(Group B). RESULTS: Ascites cultures were positive more frequently with the blood culture method(25 of 56, 44.6%) than with the conventional method(113 of 370; 30.5%) (P<0.05). Sixteen of the 56 patients in Group A had SBP and 29 had culture negative neutrocytic ascites(CNNA) while 66 of the 370 patients in Group B had SBP and 229 had CNNA The conventional method recovered more contaminating microorganisms than the blood culture method(17.7% vs 6.9%). CONCLUSIONS: The inoculation of ascitic fluid into the BACTEC blood culture bottles at the bedside is more sensitive than the conventional method of inoculation on solid media at the laboratory bench in the recovery of pathogens in SBP and should be used routinely for the optimum diagnosis of SBP.