Yang et al. reported pull-off force measurements between an atomic force microscope tip and a silicon wafer. They deduced the pressure of liquid water inside the capillary bridge formed in humid air. They claimed that their 'research shows that nanoscale water capillary bridges are metastable and have absolutely negative pressure approaching the limit of stability for water' (around -200 MPa at room temperature). Indeed, pressures reaching -160 MPa were reported, establishing a world record. However, we show that the bridges are not metastable, that the analysis used suffers from internal inconsistency, and that several assumptions made are questionable. (C) 2008 Elsevier B.V. All rights reserved.