 The tolerability and efficacy of a 3 days treatment with Ampicillin- Sulbactam AS 3g x 3 day i.v. is compared a 3 days regimen with Ertapenem 1 gday i.v.. in patients with localized peritonitis with a blinded evaluation of efficacy end points. Evaluation of cure or failure is blinded by use of designated third party individuals who are unaware of the treatment assigned to the patients. 