In order to assess the usefulness of methods for noninvasive study of respiratory mechanics in intubated patients better, we studied 16 anesthetized paralyzed mechanically ventilated guinea pigs previously sensitized with ovalbumin. Respiratory system elastance and resistance were determined in control and acute antigen exposed (AAE) animals by the end-inflation occlusion method (EIOM), the single-breath method (SBM), and the interrupter technique (IT). In control group, total respiratory system resistance and elastance were constant over tidal volume range and the three methods provided similar results. In AAE group elastance was also constant throughout tidal volume and measured by SBM and IT was, respectively, 93.4 and 57.9% higher than in control group. The relationships between resistive pressure and expiratory flow became curvilinear with an upward convexity. IT underestimated both elastance and resistance measurements in AAE group. Using EIOM the determination of the homogeneous and uneven components of respiratory resistance was possible in control animals, whereas in AAE group resistance was entirely represented by its uneven component.