Trauma to the major papilla and transient supraphysiologic biliary tract pressure during ERCP may produce transient serum liver test elevation. Further investigation of these abnormal serum tests may be costly, potentially hazardous, and unnecessary. Transient rises in post ERCP serum liver tests may be a common epiphenomenon that requires only careful clinical observation. Our aim was to study serum liver test results collected before and after ERCP in asymptomatic (or minimally symptomatic) patients and determine the natural clinical history of these patients, without further intervention. Data were collected prospectively as part of a larger study, and this subset of data on asymptomatic patients was then analyzed separately. All patients had serum liver tests done before ERCP, and 4 and 18-24 h after ERCP. Thirty-seven patients were evaluated. Sixteen of the 36 (43%) had an abnormal serum liver test after ERCP. Fifteen of the 36 had a biliary or pancreatic papillotomy done. Whether or not a patient had a papillotomy performed did not appear to influence the incidence of abnormal transient serum liver test rise. There were no biliary stents placed in any of the patients evaluated. There were two cases of post-ERCP pancreatitis (one mild; one moderate). There were no cases of cholangitis or persistent biliary tract obstruction. In conclusion, a transient rise in ERCP serum liver tests appears common following ERCP. In the absence of significant clinical signs or symptoms, these isolated serum laboratory test abnormalities should managed expectantly.