Ovalbumin induced asthma is widely accepted as an experimental model for studying pathomechanisms of allergic asthma. However, in the vast majority of the cases, pharmacological responsiveness of the airways is studied in vitro after the preparation of isolated tracheal smooth muscle strips. The present study was purported to study the in vivo reactivity of respiratory airways in experimental model of asthma induced by ovalbumin (OVA) sensitization by determininig the positive end-inspiratory pressure (PEIP) as putative in vivo marker of airways responsiveness. Adult male rats (250-300 g) were anaesthetized (sodium pentothal, 50mg/kg, i.p.; 100mg/kg/h throughout the experiment), neuromuscularly blocked (with Pancuronium bromide (2mg i.v.), and mechanically ventilated. They were randomly assigned to: a control group (CON, n=8) and a group sensitized with ovalbumin (OVA, n=8). Rats received mechanical ventilation with a tidal volume of 10 ml/kg, respiratory rate of 80-90 /min and positive end-expiratory pressure (PEEP) = 3 cmH2O. For the in vivo evaluation, an ultrasound nebulizer was mounted on the on the inspiratory circuit and PEIP was determined before and after administration of metacholine (MCH, 1 mg/ml) followed by the classic in vitro evaluation of tracheal contractile response. The reactivity of the tracheal strips was assessed in the presence of a submaximal dose of MCH (10-5 M) in isolated organ bath. PEIP after MCH was 24.75 ± 2.54 cm H2O in CON group and 39.5 ± 4.95 cm H2O in the OVA group (p < 0,001). As for the in vitro experiments, submaximal contractile responses of tracheal rings in the presence of 10-5M MCH were 0.93 ± 0.25 g force in controls vs. 1.16 ± 0.15 g force in OVA group (p<0.05) showing a corresponding degree of bronchoconstriction. The in vivo assessment of positive end-inspiratory pressure may provide a reliable modality for studying hyperreactivity of respiratory airways in the experimental model of allergic asthma in rats.