Despite improvements in surgical treatment and intensive care, mortality from severe acute pancreatitis remains high. We have carried out a randomised study of 60 consecutive patients with alcohol-induced necrotising pancreatitis to find out whether early antibiotic treatment can improve outcome. 30 patients were assigned cefuroxime (4.5 g/day intravenously) from admission. In the second group, no antibiotic treatment was given until clinical or microbiologically verified infection or after a secondary rise in C-reactive protein. The inclusion criteria were C-reactive protein concentration above 120 mg/L within 48 h of admission and low enhancement (< 30 Hounsfield units) on contrast-enhanced computed tomography. There were more infectious complications in the non-antibiotic than in the antibiotic group (mean per patient 1.8 vs 1.0, p = 0.01). The most common cause of sepsis was Staphylococcus epidermidis; positive cultures were obtained from pancreatic necrosis or the central venous line in 14 of 18 patients with suspected but blood-culture-negative sepsis. Mortality was higher in the non-antibiotic group (seven vs one in the antibiotic group; p = 0.03). Four of the eight patients who died had cultures from pancreatic necrosis positive for Staph epidermidis. We conclude that cefuroxime given early in necrotising pancreatitis is beneficial and may reduce mortality, probably by decreasing the frequency of sepsis.