This study is a double "blind" prospective evaluation of the efficacy of antibiotics (Ampicillin) in the treatment of acute alcohol-induced and idiopathic pancreatitis. Fifty-eight patients with acute pancreatitis were randomly divided into antibiotic and non-antibiotic treatment groups. The two groups were comparable clinically at the onset of the study and other than for antibiotics received identical therapy. The patients without antibiotics had a clinical course equal or slightly more favorable than the antibiotic treatment group in all parameters examined. These data indicate that prophylactic use of Ampicillin is not indicated in patients with routine acute alcohol-induced or idiopathic pancreatitis. The role of prophylactic antibiotics in patients with pancreatitis related to biliary calculi and those with more severe varieties of acute hemorrhagic or necrotizing pancreatitis remains to be more clearly defined.