Bacterial infection is without any doubt the most important risk factor in patients suffering from acute necrotizing pancreatitis determining the course of the disease, its therapeutic management and outcome. The infection route by which the bacteria enter the necroses is very likely via the colon as demonstrated by animal studies. Infection occurs very early and the frequency of infected pancreatic necrosis is about 40-70% in unselected patients. The spectrum of bacteria most frequently found are germs from the intestine, like Eschericha coli, Pseudomonas spp., Streptococcus faecalis, Enterococcus and Staphylococcus aureus. Screening for infected pancreatic necrosis is of outermost importance. In this respect fine needle aspiration by ultrasound or CT guidance with gram staining and culture is the most reliable and harmless procedure to search for infected pancreatic necrosis. Especially patients with suspected infection should undergo fine needle puncture. There is evidence that patients with acute necrotizing pancreatitis will profit by an early and appropriate antibiotic therapy. In 5/15 (33%) patients with proven acute necrotizing pancreatitis infected pancreatic necroses were found by fine needle aspiration analysis after a mean of 21 ± 3.3 days after the onset of the disease. In these patients antibiotic treatment with imipenem was started immediately after hospital admission for at least 14 days. This new concept and therapeutic approach resulted in a lower infection rate as well as delayed infection of pancreatic necrosis in the 3rd week of the disease with optimal surgical conditions in our preliminary study.