Low-dose aspirin (100 mg/day) was recently found to increase serum levels of alpha-1 protease inhibitor (A1-PI). Here, we studied the serum levels of 2 major serine protease inhibitors, A1-PI and serine leukocyte protease inhibitor (SLPI), in 10 Helicobacter pylorinegative healthy volunteers (HVs) treated with low-dose aspirin alone and in combination with other drugs.(1) Neither the treatment with low-dose aspirin alone or in combination altered serum levels of both serine protease inhibitors. The previously described increase of A1-PI levels by low-dose aspirin was most likely caused by multiple endoscopies within a few days, which caused a systemic stress response.