We studied the efficacy of gentamicin or placebo to decrease the incidence of septic complications after ERCP in 61 inpatients with possible pancreatic or biliary tract disease. The antibiotic or placebo was added to the Renograffin-60 contrast media and the study was conducted in a randomized controlled fashion. There were 29 patients who received gentamicin and 32 patients who were in the placebo group. No patient received parenteral antibiotic prior to, during, or after the ERCP unless a septic complication developed and each was followed daily with complete blood counts and oral temperatures. The incidence of febrile episodes in the gentamicin group was one (3%). All blood cultures were negative. One patient (3%) in the placebo group developed a febrile episode with subsequent blood cultures growing Escherichia coli. There was no statistical difference in the incidence of septic episodes between the two study groups. The results of this study demonstrate that the incidence of septic complications during ERCP is not modified by the addition of gentamicin to the contrast media.