Background: A rise in liver function tests (LFTs) had been noted in a patient following gastric bypass. This was studied in a subsequent gastric bypass pateint, to determine if this rise in LFTs occurred sometime between placement of the upper abdominal retractors but before the retractors were removed. Methods: LFTs were drawn preoperatively, immediately before retractor placement, immediately before retractor removal, 1 and 3 hours postoperatively, and postoperatively for 5 days until discharge. Results: LFTs rose after liver retractor placement and remained elevated for 3 days before returning to normal. Conclusions: The authors postulate that surgical retractor placement may have caused the patient's acute LFT elevation. Specifically, direct mechanical pressure may result in a transient decrease in hepatic blood-flow.