Spontaneous bacterial peritonitis (SBP) is a primary infection of asci tes without signs of perforation or penetration. It occurs most often in patients with liver cirrhosis but can also be diagnosed in patients with ascites from other causes. We report a kidney transplant recipient who developed nephrogenic ascites during an episode of acute rejection. The patient complained of fever, abdominal tenderness, and loose stools and showed all of the signs of peritonitis on physical examination. The patient's serum creatinine was elevated, and Duplex sonography of the graft was highly suggestive for acute rejection. Ascites puncture was performed. The ascitic fluid contained 4,000 leukocytes per microliter. No source of infection was detected, so the diagnosis of SBP was made. The patient was treated with ciprofloxacin intravenously and received low-dose steroid pulse therapy. The ascites culture grew Staphylococcus aureus that was highly sensitive to ciprofloxacin. The patient recovered rapidly. We could avoid laparotomy, which is associated with high mortality in patients suffering from SBP. No relapses of SBP occurred. Renal function has improved and remained stable.