Severe intraoperative hypotension has been reported in patients on angiotensin-converting enzyme inhibitors and angiotensin II receptor subtype 1 antagonists. We describe a patient on lisinopril who developed refractory intraoperative hypotension associated with increased serum tryptase level suggesting mast cell activation (allergic reaction). However, allergology workup ruled out an allergic etiology as well as mastocytosis, and hypotension recalcitrant to treatment was attributed to uninterrupted lisinopril therapy. Elevated serum tryptase was attributed to our patient's chronic renal insufficiency.