In a retrospective review of 300 children with nephrotic syndrome seen at National Taiwan University Hospital throughout the 12-year period from 1978 to 1990, 20 episodes of peritonitis were identified in 17 patients (7.4%). Gram-negative bacilli (E. coli and Klebsiella pneumoniae) were the majority of pathogens, accounting for 55% of all the cases. Streptococcus pneumoniae were cultured from only 15% of the patients. An additional 15% had negative culture results, but were clinically responsive to penicillin. In 15% of cases the cause was unknown. Clinically, peritonitis was characterized by abdominal pain (100%), abdominal tenderness (100%), rebounding pain (85%), leukocytosis (85%), and fever (75%). Based on this data, it seems reasonable to initiate antimicrobial therapy in nephrotic children with suspected peritonitis, using a combination of penicillin plus either an aminoglycoside or a broad-spectrum cephalosporin. This regimen should be continued until culture results are available.