Rationale: Methacholine (Mch) is routinely used to assess bronchial hyperreactivity, however, little is known on the differences in the lung response pattern between this provocation and that observed with ovalbumin (Ova) following allergic sensitization. Objectives: To compare i) the central vs. peripheral effects of Mch and Ova within the lung by combining measurements of airway and tissue mechanics with synchrotron radiation (SR) imaging; and ii) to assess the extent to which mechanical and imaging parameters are correlated. Methods: We used the low-frequency forced oscillation technique (LFOT) and SR imaging in control (n=12) and ovalbumin-sensitized (n=13) rabbits, at baseline, during IV Mch infusion (2.5µg/kg/min, 5.0µg/kg/min or 10.0µg/kg/min), after recovery from Mch, and following IV Ova injection (2.0 mg). We compared IV Mch challenge with inhaled Mch (125 mg/ml, 90 s) in a separate group of controls (n=5). Measurements and Main Results: Airway conductance (Gaw) and tissue elastance (H) were measured by LFOT. The central airway cross-sectional area (CAaw), the ventilated alveolar area (VA), and the heterogeneity of specific ventilation were quantified by SR imaging. Mch infusion induced constriction predominantly in the central airways, whereas Ova provocation affected mainly the peripheral airways, leading to severe ventilation heterogeneities in sensitized animals. Mch inhalation affected both conducting and peripheral airways. The correlations between Gaw and CAaw (R=0.71) and between H and VA (R=-0.80) were strong. Conclusions: The pattern of lung response caused by IV Mch and Ova are fundamentally different. Although inhaled Mch induces a heterogeneous lung response similar to that observed with IV allergen, these similar patterns are due to different mechanisms.