Introduction Inappropriate accumulation of eosinophils and the subsequent release of their potent armoury of mediators are thought to contribute significantly to the airway inflammation underlying asthma pathogenesis. Montelukast (MLK) is a cysteinyl leukotriene receptor-1 (CysLT1) antagonist that is an effective treatment for asthma and other allergic conditions. However, MLK may possess anti-inflammatory effects independent of CysLT1 antagonism. Aims We assessed real-time resting and GM-CSF-stimulated eosinophil adhesive behaviour together with effect of MLK on eosinophil adhesion to recombinant human vascular cell adhesion molecule-1 (rhVCAM-1) at different rates of flow using a novel microflow system. Methods The flow system consists of a syringe pump and flow sensor controlled by a PC using dedicated software linked to a microfluidic biochip with 8-channels whose dimensions mimic the post-capillary venules [1]. The microfluidic syringe pump gives very accurate flow rates that are more reproducible and consistent than anything currently available and those used in this study (1-5 dyn cm-2) mimic those found in the post-capillary venules during inflammatory processes. Eosinophils were purified using our standard technique using dextran sedimentation and centrifugation on Percoll gradients followed by CD16-dependent negative immunomagnetic selection [2]. Resting or GM-CSF-stimulated eosinophils were pre-incubated with a concentration range of MLK before being pumped through the VCAM-1-coated channels at increasing rates of shear stress. Adherent eosinophils were microscopically recorded in real time and analysed using DucoCell software. Results & Conclusions At 1 or 2 dyn cm-2 shear stress resting eosinophils either tethered immediately to rhVCAM-1, “rolled” along part of the channel until tethering took place, or roll without tethering. At flow rates greater than 2 dyn cm-2, adherent eosinophils began to be displaced from rhVCAM-1. MLK (10nM and 100nM) significantly inhibited resting eosinophil adhesion to rhVCAM-1 at 2 dyn cm-2 shear stress (40.5±9.9% and 47.8±9.4% inhibition respectively; P<0.05). GM-CSF-stimulated eosinophil adhesion at 2 dyn/cm2 was characterised by greater cell flattening with significant inhibition by 10nM MT (22.2±5.4%, P<0.05 compared to control). These findings demonstrate inhibition of eosinophil adhesion to VCAM-1 by MLK under shear stress at physiologically relevant concentrations indicating a potential anti-asthmatic action independent of CysLT1 antagonism.